Methods for promoting hematopoietic reconstitution

ABSTRACT

The present invention provides for compositions and methods for modulating hematopoetic stem cell populations by using HCS modulators, which are agents that either increase HSC numbers or decrease HSC numbers as desired by a particular indication. For example, HSC modulators found to increase HSC numbers include prostaglandin E 2  (PGE2) and agents that stimulate the PGE2 pathway. Conversely, HSC modulators that prevent PGE2 synthesis decrease HSC numbers. HCS modulators may be used in vitro, in vivo, or ex vivo.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. Ser. No.12/294,344 filed on Jul. 10, 2009, which is a 35 U.S.C. §371 NationalPhase Entry of International Application No. PCT/US2007/007419 filed onMar. 26, 2007, which designates the United States, and which claimsbenefit under 35 U.S.C. §119(e) of U.S. Provisional Application No.60/785,968 filed on Mar. 24, 2006, the contents of each of which areincorporated herein by reference in their entireties.

GOVERNMENT SUPPORT

This invention was supported by the National Institutes of Health—NIHGrant No. CA103846-02. The government of the United States has certainrights in this invention.

FIELD OF THE INVENTION

The present embodiments provide for modulators that either increase ordecrease hematopoeitic stem cell populations in vitro, in vivo, and exvivo.

BACKGROUND

Stem cell research holds extraordinary potential for the development oftherapies that may change the future for those suffering from diseasessuch as leukemia, diabetes, and anemia. Much research focuses on theexploration of stem cell biology as a key to treatments for diseases.Through an understanding of the role of stem cells in normaldevelopment, researchers seek to capture and direct the innatecapabilities of stem cells to treat many conditions. Research ison-going in a number of areas simultaneously: examining the genetic andmolecular triggers that drive embryonic stem cells to develop in varioustissues; learning how to push those cells to divide and form specializedtissues; culturing embryonic stem cells and developing new lines to workwith; searching for ways to eliminate or control Graft Vs. Host Diseaseby eliminating the need for donors; and generating a line of universallytransplantable cells.

Hematopoietic stem cells (HSCs) are derived during embryogenesis indistinct regions where specific inductive events convert mesoderm toblood stem cells and progenitors. There remains a need to elucidate therelationships between particular biomolecules, chemical agents, andother factors in these inductive events. For example, there remains aneed to identify which biomolecules or chemical agents show promise inmanipulating the HSC population for a desired purpose, such asincreasing a HCS population for research or therapeutics.

SUMMARY

The compositions and methods of the present embodiments provide for HCSmodulators, which are agents that either increase HSC numbers ordecrease HSC numbers as desired by a particular indication. For example,HSC modulators found to increase HSC numbers include prostaglandin E2(PGE2) and agents that stimulate the PGE2 pathway. Conversely, HSCmodulators that prevent PGE2 synthesis decrease HSC numbers.

One embodiment provides a method for promoting hematopoietic stem cellgrowth in a subject, comprising administering at least one hematopoieticstem cell (HSC) modulator and a pharmaceutically acceptable carrier.

In another embodiment, the HSC modulator increases HSCs by modifying theprostaglandin pathway. A HSC modulator that enhances HCS populations bymodifying the prostaglandin pathway may be at least one compoundselected from the group consisting of PGE2, dmPGE2, PGI2, Linoleic Acid,13(s)-HODE, LY171883, Mead Acid, Eicosatrienoic Acid,Epoxyeicosatrienoic Acid, ONO-259, Cay1039, a PGE2 receptor agonist, anda derivative of any of these agents. In a more particular embodiment,the HSC modulator is a PGE2 derivative selected from the groupconsisting of 16,16-dimethyl PGE2, 19(R)-hydroxy PGE2, 16,16-dimethylPGE2 p-(p-acetamidobenzamido) phenyl ester, 11 deoxy-16,16-dimethylPGE2, 9-deoxy-9-methylene-16,16-dimethyl PGE2, 9-deoxy-9-methylene PGE2,Butaprost, Sulprostone, PGE2 serinol amide, PGE2 methyl ester, 16-phenyltetranor PGE2, 15(S)-15-methyl PGE2, and 15(R)-15-methyl PGE2.

In another embodiment, the HSC modulator increases HSCs by modifying theWnt pathway. A HSC modulator that enhances HCS populations by modifyingthe wnt pathway may be at least compound selected from the groupconsisting of PGE2, dmPGE2, BIO, LiCl, and derivatives of thesecompounds.

In yet another embodiment, the HSC modulator increases HSCs by modifyingcAMP/P13K/AKT second messenger. A HSC modulator that enhances HCSpopulations by modifying cAMP/P13K/AKT second messenger may be at leastone compound selected from the group consisting of 8-bromo-cAMP,Forskolin, and derivatives of these agents.

In still another embodiment, the HSC modulator increases HCS populationsby modifying Ca2+ second messenger. A HCS modulator that enhances HCSpopulations by modifying Ca2+ second messenger may be at least one agentselected from the group consisting of Bapta-AM,Fendiline, Nicardipineand derivatives of these compounds.

In another embodiment, the HSC modulator increases HSCs by modifyingNO/Angiotensin signaling. A HCS modulator that enhances HCS populationsby modifying NO/Angiotensin signaling may be at least one compoundselected from the group consisting of L-Arg, Sodium Nitroprus side,Sodium Vanadate, Bradykinin, and derivatives thereof.

In yet another embodiment, the HSC modulator that enhances HCSpopulations may be at least one agent selected from the group consistingof Mebeverine, Flurandrenolide, Atenolol, Pindolol, Gaboxadol, KynurenicAcid, Hydralazine, Thiabendazole, Bicuclline, Vesamicol, Peruvoside,Imipramine, Chlorpropamide, 1,5-Pentamethylenetetrazole,4-Aminopyridine, Diazoxide, Benfotiamine, 12-Methoxydodecenoic acid,N-Formyl-Met-Leu-Phe, Gallamine, IAA 94, Chlorotrianisene, andderivatives of these compounds.

Another embodiment provides a method for promoting HSC growth bycontacting a nascent stem cell population with at least one compoundselected from the group consisting of PGE2, PGI2, Linoleic Acid,13(s)-HODE, LY171883, Mead Acid, Eicosatrienoic Acid,Epoxyeicosatrienoic Acid, ONO-259, Cay1039, a PGE2 receptor agonist, of16,16-dimethyl PGE2, 19(R)-hydroxy PGE2, 16,16-dimethyl PGE2p-(p-acetamidobenzamido) phenyl ester, 11-deoxy-16,16-dimethyl PGE2,9-deoxy-9-methylene-16,16-dimethyl PGE2, 9-deoxy-9-methylene PGE2,Butaprost, Sulprostone, PGE2 serinol amide, PGE2 methyl ester, 16-phenyltetranor PGE2, 15(S)-15-methyl PGE2, 15(R)-15-methyl PGE2, BIO,8-bromo-cAMP, Forskolin, Bapta-AM, Fendiline, Nicardipine, Nifedipine,Pimozide, Strophanthidin, Lanatoside, L-Arg, Sodium Nitroprus side,Sodium Vanadate, Bradykinin, Mebeverine, Flurandrenolide, Atenolol,Pindolol, Gaboxadol, Kynurenic Acid, Hydralazine, Thiabendazole,Bicuclline, Vesamicol, Peruvoside, Imipramine, Chlorpropamide,1,5-Pentamethylenetetrazole, 4-Aminopyridine, Diazoxide, Benfotiamine,12-Methoxydodecenoic acid, N-Formyl-Met-Leu-Phe, Gallamine, IAA 94,Chlorotrianisene, and derivatives thereof. The nascent stem cellpopulation may be collected from peripheral blood, cord blood, chorionicvilli, amniotic fluid, placental blood, or bone marrow.

Another embodiment of the present invention provides a method forpromoting HSC expansion ex vivo, comprising incubating HSC in thepresence of at least one HSC modulator. Another embodiment of thepresent invention provides a method for promoting HSC expansion ex vivo,comprising collecting HSC source sample (e.g., peripheral blood, cordblood, amniotic fluid, placental blood, bone marrow, chorionic villi)and storing it in the presence of at least one HSC modulator such asPGE2. A particular embodiment provides for a kit comprising a containersuitable for HCS-source sample storage in which the container ispre-loaded with at least one HSC modulator that increases HCSs. Anadditional embodiment provides a kit comprising a container suitable forHCS-source sample storage and a vial containing a suitable amount of atleast one HSC modulator that increases HSCs. A further embodiment of thepresent invention provides a method for promoting HSC expansion ex vivo,in which the nascent HSC source is contacted with PGE2, or a derivativethereof, at initial collection, during processing, at storage, uponthawing, or during transfusion.

In another embodiment of the present invention, the HSC modulatorinhibits HSCs by modifying the prostaglandin pathway. A HSC modulatorthat inhibits HCS populations by modifying the prostaglandin pathway maybe at least one compound selected from the group consisting ofIndomethacin, Fenbufen, NS398, SC560, Sulindac, Suxibuzone, Aspirin,Naproxen, Ibuprofen, Celecoxib, PGD2, Aristolochic Acid, AH6809,AH23848, and derivatives of these.

In another embodiment, the HSC modulator inhibits HSCs by modifying theWnt pathway. A HSC modulator that inhibits HCS populations by modifyingthe Wnt pathway may be at least one of the agents selected from thegroup consisting of prostaglandin inhibitors, Kenpaullone, ValproicAcid,or a derivative thereof.

In yet another embodiment of the present invention, the HSC modulatorinhibits HSCs by modifying cAMP/P13K/AKT second messenger. A HSCmodulator that inhibits HCS populations by modifying the cAMP/P13K/AKTsecond messenger may be one or more compounds selected from the groupconsisting of PD98059, KT5720, H89, U0126, Wortmannin, and derivativethereof.

In another embodiment, the HSC modulator inhibits HSCs by modifying Ca2+second messenger. A HSC modulator that inhibits HCS populations bymodifying the Ca2+ second messenger may be at least one agent selectedfrom the group consisting of BayK-8644, Thioridazine, and derivative ofthese agents.

In still another embodiment, the HSC modulator inhibits HSCs bymodifying NO/Angiotensin signaling. A HSC modulator that inhibits HCSpopulations by modifying NO/Angiotensin signaling may be at least onecompound selected from the group consisting of L-NAME, Enalapril,Captopril, AcSDKP, Losartan, AcSDKP, Losartan, Telimasartan, Histamine,Ambroxol, Chrysin, Cycloheximide, Methylene Blue, Epinephrine,Dexamethazone, Proadifen, Benzyl isothiocyanate, Ephedrine, andderivatives thereof.

In an additional embodiment of the invention, the HSC modulator thatinhibits HCS populations is at least one compound selected from thegroup consisting of Paragyline, Propranolol, Etanidazole, Methimazole,Cinoxacin, Penicillamine, Furosemide, Eburnamininone, Aclarubicin,Warfarin, Gamma-aminobutyric Acid, Norethindrone, Lupinidine,Hydroquinidine, Todralazine, Methoxamine, Hydroxyurea,Dihydroergotamine, Antazoline, 3-Nitropropionic Acid,N-Phenylanthranilic Acid, Phenazopyridine, Dichlorokynurenic acid,3-estradiol, L-Leu, Phenoxybenzamine, Mephentermine, Guvacine,Guaiazulene, Imidazole, Beta-Carotene, Clofibrate, and derivatives ofthese compounds.

Yet another embodiment provides for a method for inhibiting HSC growthin a subject, comprising administering at least one HSC modulator and apharmaceutically acceptable carrier. In a particular embodiment, the HSCmodulator is one or more of the compounds selected from the groupconsisting of Indomethacin, Celecoxib, Fenbufen, Prosteglandin J2,Suxibuzone, Sulindac, and derivatives thereof.

Another embodiment provides a method for decreasing HSC growth bycontacting a nascent stem cell population with at least one compoundselected from the group consisting of Indomethacin, Fenbufen, NS398,SC560, Sulindac, Suxibuzone, Aspirin, Naproxen, Ibuprofen, Celecoxib,PGD2, Aristolochic Acid, AH6809, AH23848, Kenpaullone, Valproic Acid,PD98059, KT5720, H89, U0126, Wortmannin, BayK 8644, Thiridazine, L-NAME,Enalapril, Captopril, AcSDKP, Losartan, AcSDKP, Losartan, Telimasartan,Histamine, Ambroxol, Chrysin, Cycloheximide, Methylene Blue,Epinephrine, Dexamethazone, Proadifen, Benzyl isothiocyanate, Ephedrine,Paragyline, Propranolol, Etanidazole, Methimazole, Cinoxacin,Penicillamine, Furosemide, Eburnamininone, Aclarubicin, Warfarin,Gamma-aminobutyric Acid, Norethindrone, Lupinidine, Hydroquinidine,Todralazine, Methoxamine, Hydroxyurea, Dihydroergotamine, Antazoline,3-Nitropropionic Acid, N-Phenylanthranilic Acid, Phenazopyridine,Dichlorokynurenic acid, 3-estradiol, L-Leu, Phenoxybenzamine,Mephentermine, Guvacine, Guaiazulene, Imidazole, Beta-Carotene,Clofibrate, a PGE2 receptor antagonist, and derivatives of thesecompounds.

DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a schematic of a screen for chemicals that affect stemcells in the AGM using Zebrafish embryos.

FIGS. 2A and 2B relate to prostaglandin agonists and antagonists thatalter runx1/cmyb expression without affecting vascular development. FIG.2A shows microarray expression profiles of FACS sorted cell populationsisolated during primitive (gata1 and lmo2) and definitive (lmo2 andcd41) hematopoiesis. Relative expression of cox1 (light gray) and cox-2(dark gray) in each GFP+ sorted fraction compared to GFP− cells isshown. FIG. 2B shows the qPCR profiles of endothelial and HSC specificgene expression following exposure to long-acting dmPGE2 (10 μM, secondbar in each triplet, dark gray) or the nonspecific cox inhibitorindomethacin (10 μM, third bar in triplet) versus control (first bar intriplet). Both treatments resulted in statistically significantdifferences compared to controls for each gene examined (ANOVA, p<0.05,n=8).

FIG. 3 depicts data indicating that prostaglandin agonists andantagonists alter runx1/cmyb expression by quantitative analysis of HSCnumbers in bigenic zebrafish embryos detected by confocal microscopy:DMSO 23.3±5.0 (mean±SD), dmPGE2 (10 □M) 38.0±2.2, indomethacin (10 □M)(ANOVA, p<0.00001, n=10/treatment).

FIGS. 4A and 4B show that treatment with dmPGE2 enhances hematopoieticrecovery in sublethally irradiated adult zebrafish. Zebrafish whole KMirradiation recovery experiments were performed. Asterisks (*) indicatestatistically significant differences: *=50 μM vs control, **=50 μM vs10 μM and 50 μM vs control, ***=all variables significant (ANOVA,p<0.05, n=15/variable). FIG. 4A shows representative FSC/SSC FACSprofiles of hematopoietic cell lineages in the KM on days 0, 4, 7, 10and 14 of irradiation recovery in DMSO and dmPGE2-treated (50 μM)zebrafish. FIG. 4B shows kinetics of KM reconstitution of precursor,lymphoid and myeloid cells in control fish (triangle) and dmPGE2-treatedfish (square, 10 μM; circle, 50 μM).

FIGS. 5A and 5B depict modulation of PG pathway that alters expressionof HSC-related genes and recovery in sublethally irradiated adultzebrafish. FIG. 5A shows the effect of dmPGE2 treatment on stem cell andendothelial markers, as measured by qPCR on whole KM isolated on daythree post-irradiation. An asterisk (*) indicates a statisticallysignificant difference (two-tailed t-test, n=15, runx1: p=0.0001; 1 mo2:p=0.014; fli1: p=0.049). FIG. 5B depicts the effect of cox1 (SC560, 100M) and cox2 (NS398, 10 ␣M) inhibition on irradiation recovery(n=5/treatment). For fish treated with SC560 or NS398 no analysis couldbe obtained at day fourteen due to excessive death in these treatmentgroups.

FIGS. 6A and 6B show that dmPGE2 modulates colony number andhematopoietic differentiation in mouse ES cells. M3434 and OP9 ES cellcolony forming assays were performed; counts are per 100,000 cellsplated. The bars indicate control-treated ES cells and treatment withincreasing doses of dmPGE2 (10 μM, 20 μM, 100 μM) orindomethacin-treated (10 μM, 100 μM) ES cells. An asterisk (*) indicatesa statistically significant difference (two-tailed t-test,n=5/variable). FIG. 6A, Effect of increasing doses of dmPGE2 andinhibition of cyclooxygenase activity by indomethacin on hematopoieticdifferentiation in methylcellulose; numbers of definitive erythroid (E),mixed granulocyte/monocyte (GM), and multi-potent (GEMM) progenitorcolonies are shown (10 μM dmPGE2: GM p=0.005, GEMM p=0.017; 20 μMdmPGE2: dE p=0.04, GM p=0.007, GEMM 0.016; 100 μM indomethacin: GMp=0.024). FIG. 6B, Effect of dmPGE2 and indomethacin on OP9hematopoietic colony number (20 μM: p=0.047).

FIGS. 7A and 7B depict PGE2 influences on colony number. Morespecifically, FIGS. 7A and 7B illustrate dmPGE2-mediated (10 μM) rescueof indomethacin (100 μM) inhibition of colony formation in (A)methylcellulose and (B) OP9 assays.

FIGS. 8A-FIG. 8F indicate that exposure of murine BM to dmPGE2 increasesthe number of CFU-S and repopulating HSCs. An asterisk (*) indicates astatistically significant difference. FIGS. 8A and 8B, Effect of ex vivotreatment of WBM (2 hrs on ice) with EtOH control or dmPGE2 (1 μM/106cells) on CFU-S8 and CFU-S12 (60,000 cells/recipient; CFU-512:two-tailed t-test, n=10, p<0.0001). FIG. 8C, Effect on CFU-S12 followingex vivo treatment with indomethacin (1 ρM/106 cells) (100,000cells/recipient; two-tailed t-test, n=10, p=0.0002). FIG. 8D, CFU-S12evaluation after treatment of ckit+scal+lineage-stem cells with dmPGE2or EtOH control (two-tailed t-test, 100 cells: n=10, p=0.013; 300 cells:p=0.0003). FIGS. 8E and 8F, Limiting dilution competitive repopulationassay. The number of negative recipients as determined by FACS analysis(e) in relation to the total number of cells transplanted for control(square) or dmPGE2-treated (circle) cell samples is shown at 12 weeks.The frequency of engraftment (Panel F) at 6, 12, an 24 weeks posttransplantation in recipients of EtOH versus dmPGE2-treated WBMcalculated by Poisson statistics (ANOVA, n=10/variable, 6 wks: p=0.005;12 wks: p=0.002; 24 wks: p=0.05); the number of recipients surviving toanalysis at each time point is shown in Table 6-Table 8.

FIGS. 9A-9N depict data showing that exposure of murine BM to dmPGE2increases spleen weight and 1 HSC engraftments. FIGS. 9A and 9B, Effectof ex vivo treatment of WBM and isolated HSCs with EtOH control ordmPGE2 on spleen weight on day (a) eight and (b) twelve (two-tailedt-test, CFU-S8: n=5, p=0.339; CFU-S12: n=9, p<0.00001). FIG. 9C, Splenicweight following indomethacin treatment (green) compared to control(two-tailed t-test: n=10, p=0.00026). FIG. 9D, Spleen colony numberafter dmPGE2 treatment of KSL cells (two-tailed t-test, 100 cells: n=4,p=0.0013; 300 cells: n=5, p=0.009). FIG. 9E, Representative FACS plotsillustrating the levels of CD45.1 engraftment (upper left quadrant) inrecipients of control and dmPGE2 exposed BM cells. FIGS. 9F-9J, Averagechimerism (F, H, I) and calculated frequency of engraftment (FIGS. 9Gand 9J) in recipients of dmPGE2-treated WBM (circles) versus control(squares). FIGS. 9K and 9L, Effect of ex vivo treatment of WBM with cox1(SC560, 10□M) and cox2 (NS398, 10 □M) inhibitors in the CFU-S12 assay oncolony number (paired t-test, n=10, SC560 p=0.00016, NS398 p<0.00001 andsplenic weight (paired t-test, n=10, SC560 p=0.025, NS398 p=0.00075).FIGS. 9M and 9N, Peripheral blood (day 14 post treatment) and bonemarrow (day 16 post treatment) WBC counts following 5-FU bone marrowinjury; in vivo exposure to SC560 or NS398 significantly inhibited WBCrecovery, while dmPGE2 enhanced WBC counts.

FIG. 10 presents a diagram of the Wnt signaling pathway.

FIGS. 11A and 11B depict data that the modulation of wnt activityaffects adult homeostasis. FIG. 11A shows a schematic of the irradiationassay; FIG. 11B presents FACS analysis of whole kidney marrow on day tenpost irradiation in wt, hs:wnt8, hs:dkk and hs:dnTCF adults.

FIG. 12 shows qPCR quantification of the alterations in wnt activity inthe developing embryo caused by prostaglandin signaling in an in vivoTop:dGFP assay.

FIG. 13 presents a model depicting the potential points of interactionof the PG and wnt pathways. (1) PGE2 can not rescue dkk, axin, dnTCF;indomethacin can not block wnt8. (2) PGE2 rescues dkk, but not axin anddnTCF; indomethicin can block wnt8; PGE2 rescues dkk and axin, but notdnTCF; indomethacin can block wnt8. (4) PGE2 rescues dkk, axin anddnTCF; indomethacin can block wnt8.

FIG. 14 shows the percent of GFP positive cells in the kidney marrow ofTop:dGFP adults at day three following irradiation and treatment withdmPGE2 or indomethacin.

DETAILED DESCRIPTION

Unless otherwise defined herein, scientific and technical terms used inconnection with the present application shall have the meanings that arecommonly understood by those of ordinary skill in the art. Further,unless otherwise required by context, singular terms shall includepluralities and plural terms shall include the singular.

It should be understood that this invention is not limited to theparticular methodology, protocols, and reagents, etc., described hereinand as such may vary. The terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to limit thescope of the present invention, which is defined solely by the claims.

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients or reaction conditions usedherein should be understood as modified in all instances by the term“about.” The term “about” when used in connection with percentages maymean±1%.

All patents and other publications identified are expressly incorporatedherein by reference for the purpose of describing and disclosing, forexample, the methodologies described in such publications that might beused in connection with the present invention. These publications areprovided solely for their disclosure prior to the filing date of thepresent application. Nothing in this regard should be construed as anadmission that the inventors are not entitled to antedate suchdisclosure by virtue of prior invention or for any other reason. Allstatements as to the date or representation as to the contents of thesedocuments is based on the information available to the applicants anddoes not constitute any admission as to the correctness of the dates orcontents of these documents.

Hematopoietic stem cell (HSC) homeostasis it tightly controlled bygrowth factors, signaling molecules, and transcription factors.Definitive HCSs derived during embryogenesis in theaorta-gonad-mesonephros (AGM) region subsequently colonize the niche infetal and adult hematopoietic organs. Dzierzak, 12 Curr. Opin. Hematol.197-202 (2004); Galloway & Zon, 53 Curr. Top. Devel. Biol. 139-58(2003).

The present invention provides methods for modulating HSC growth andrenewal in vitro, in vivo, or ex vivo. The method comprises contacting anascent stem cell population with at least one HSC modulator. Thispopulation may be contained within peripheral blood, cord blood, bonemarrow, amniotic fluid, chorionic villa, placenta, or otherhematopoietic stem cell niches. In one embodiment, the inventionprovides methods for promoting hematopoietic stem growth and renewal ina cell population. In another embodiment, the invention provides methodsfor inhibiting hematopoietic stem cell growth and renewal in a cellpopulation.

The present invention is based, in part, on the discovery PGE2 andagents that enhance PGE2 synthesis cause an increase in HSC numbers.Conversely, agents that block PGE2 synthesis decrease HSCs. In thatregard, agents affecting PGE2 synthesis may be considered HSCmodulators. For example, the cyclooxygenases (cox) responsible for PGE2synthesis may be required for HSC formation. Additionally, vasodilatoragents promote HSC expansion, conversely, vasoconstrictors decrease HSCnumbers. For example, hydralazine, an anti-hypertensive vasodialator,increased HSCs while fenbufen, a nonsteroidal anti-inflammatory drugvasoconstrictor decreased HSCs. These agents are thus also consideredHSC modulators.

As used herein, HSC modulators may either promote or inhibit HSC growthand renewal. HSC modulators influence HSC numbers in a cell population.HSC modulators influence HSC expansion in culture (in vitro), duringshort term incubation, (ex vivo) or in vivo. See Table 1, below. HSCmodulators that increase HSC numbers include agents that upregulate PGE2synthesis. An increase in HSC numbers can be an increase of about 10%,about 20%, about 30%, about 40%, about 50%, about 60%, about 70%, about80%, about 90%, about 100%, about 150%, about 200% or more, than the HSCnumbers exhibited by the subject prior to treatment.

HSC modulators that cause a decrease in HSC numbers down-regulate PGE2synthesis and/or promote vasoconstriction. See, for example, Table 2,below. A decrease in HSC numbers can be a decrease of about 10%, about20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%,about 90%, about 100%, about 150%, about 200% or more, than the HSCnumbers exhibited by the subject prior to treatment. HSC numbers may beevaluated by the alleviation of the symptoms of the disease, forexample, increased platelet count, increased hematocrit, whereinplatelet count or hematocrit is increased about 10%, about 20%, about30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%,about 100%, about 150%, about 200% or more. The effect on HSC numbersmay be evaluated by the alleviation of the symptoms of the disease, forexample, increased platelet count, increased hematocrit, whereinplatelet count or hematocrit is increased about 10%, about 20%, about30%, about 40%, about 50%, about 60%, about 70%, about 80%, about 90%,about 100%, about 150%, about 200% or more.

In one embodiment, PGE2 or dmPGE2 are used as HSC modulators to increasethe HSC population.

The HCS modulators of the present invention also include derivatives ofHCS modulators. Derivatives, as used herein, include a chemicallymodified compound wherein the modification is considered routine by theordinary skilled chemist, such as additional chemical moieties (e.g., anester or an amide of an acid, protecting groups, such as a benzyl groupfor an alcohol or thiol, and tert-butoxycarbonyl group for an amine).Derivatives also include radioactively labeled HSC modulators,conjugates of HSC modulators (e.g., biotin or avidin, with enzymes suchas horseradish peroxidase and the like, with bioluminescent agents,chemoluminescent agents or fluorescent agents). Additionally, moietiesmay be added to the HCS modulator or a portion thereof to increasehalf-life in vivo. Derivatives, as used herein, also encompassesanalogs, such as a compound that comprises a chemically modified form ofa specific compound or class thereof, and that maintains thepharmaceutical and/or pharmacological activities characteristic of saidcompound or class, are also encompassed in the present invention.Derivatives, as used herein, also encompasses prodrugs of the HCSmodulators, which are known to enhance numerous desirable qualities ofpharmaceuticals (e.g., solubility, bioavailability, manufacturing,etc.).

Direct ex vivo administration of HSC modulators can enable significantin vivo expansion of hematopoietic stem cells, such that even smalleramounts of hematopoietic stem cells can then be enough intransplantation. Consequently, for example, cord blood stem celltransplantation may now be applied to not only children but also adults.Such stem cells may be collected from sources including, for example,peripheral blood, cord blood, bone marrow, amniotic fluid, or placentalblood. Alternatively, the HSC-containing source sample may be harvestedand then stored immediately in the presence of a HSC modulator, such asPGE2, and initially incubated (prior to differentiation) in the presenceof the HSC modulator before introduction into a subject.

Additionally, one or more HSC modulators can be used in vivo to increasethe number of stem cells in bone marrow or other sources (such as cordblood). By increasing the number of stem cells, the total harvest ofstem cells from the subject can be significantly improved. Further, byincreasing the number of stem cells harvested from the subject, thenumber of stem cells available for transplantation back into the subjector to another subject can also be significantly improved, therebypotentially reducing the time to engraftment, and consequently leadingto a decrease in the time during which the subject has insufficientneutrophils and platelets, thus preventing infections, bleeding, orother complications.

In addition, the present invention can reduce the proportion of subjectswho are otherwise unable to mobilize enough cells for stem cell harvestto proceed with treatment for their primary illness, e.g., chemotherapyand other bone marrow ablative treatments. Thus, the proportion of thenumber of subjects with delayed primary engraftment can also be reduced.Furthermore, the present invention can promote recovery subsequent tobone marrow ablative treatments by increasing HSC numbers.

HSC modulators, such as those in Table 1 and disclosed herein, can beused in vivo to increase HSC production and ex vivo to increase HSCnumber. This is accomplished by administering one or more of thecompounds to a subject or to the stem cells.

HSC modulators can also be used to provide autologous HSCs to a subject.Typically, this involves the steps of administering HSC modulators to asubject in need thereof to enhance expansion of the stem cell populationwithin bone marrow and/or to mobilize the stem cells in peripheralcirculation; harvesting one or more of the bone marrow stem cells or oneor more of the stem cells in the peripheral circulation; andtransplanting the one or more harvested stem cells back into thesubject.

In addition, the stem cells obtained from harvesting according to methodof the present invention described above can be cryopreserved usingtechniques known in the art for stem cell cryopreservation. Accordingly,using cryopreservation, the stem cells can be maintained such that onceit is determined that a subject is in need of stem cell transplantation,the stem cells can be thawed and transplanted back into the subject. Asnoted previously, the use of one or more HSC modulators, for examplePGE2, during cryopreservation techniques may enhance the HSC population.

More specifically, another embodiment of the present invention providesfor the enhancement of HSCs collected from cord blood or an equivalentneonatal or fetal stem cell source, which may be cryopreserved, for thetherapeutic uses of such stem cells upon thawing. Such blood may becollected by several methods known in the art. For example, becauseumbilical cord blood is a rich source of HSCs (see Nakahata & Ogawa, 70J. Clin. Invest. 1324-28 (1982); Prindull et al., 67 Acta. Paediatr.Scand. 413-16 (1978); Tchernia et al., 97(3) J. Lab. Clin. Med. 322-31(1981)), an excellent source for neonatal blood is the umbilical cordand placenta. The neonatal blood may be obtained by direct drainage fromthe cord and/or by needle aspiration from the delivered placenta at theroot and at distended veins. See, e.g., U.S. Pat. No. 7,160,714; U.S.Pat. No. 5,114,672; U.S. Pat. No. 5,004,681; U.S. patent applicationSer. No. 10/076180, Pub. No. 20030032179.

Indeed, umbilical cord blood stem cells have been used to reconstitutehematopoiesis in children with malignant and nonmalignant diseases aftertreatment with myeloablative doses of chemo-radiotherapy. Sirchia &Rebulla, 84 Haematologica 738-47 (1999). See also Laughlin 27 BoneMarrow Transplant. 1-6 (2001); U.S. Pat. No. 6,852,534. Additionally, ithas been reported that stem and progenitor cells in cord blood appear tohave a greater proliferative capacity in culture than those in adultbone marrow. Salahuddin et al., 58 Blood 931-38 (1981); Cappellini etal., 57 Brit. J. Haematol. 61-70 (1984).

Alternatively, fetal blood can be taken from the fetal circulation atthe placental root with the use of a needle guided by ultrasound (Daffoset al., 153 Am. J. Obstet. Gynecol. 655-60 (1985); Daffos et al., 146Am. J. Obstet. Gynecol. 985-87 (1983), by placentocentesis (Valenti,115Am. J. Obstet. Gynecol. 851-53 (1973); Cao et al., 19 J. Med. Genet.81-87 (1982)), by fetoscopy (Rodeck, in Prenatal Diagnosis, (Rodeck &Nicolaides, eds., Royal College of Obstetricians & Gynaecologists,London, 1984)). Indeed, the chorionic villus and amniotic fluid, inaddition to cord blood and placenta, are sources of pluripotent fetalstem cells (see WO 2003 042405) that may be treated by the HCSmodulators of the present invention.

Various kits and collection devices are known for the collection,processing, and storage of cord blood. See, e.g., U.S. Pat. No.7,147,626; U.S. Pat. No. 7,131,958. Collections should be made understerile conditions, and the blood may be treated with an anticoagulant.Such an anticoagulants include citrate-phosphate-dextrose, acidcitrate-dextrose, Alsever's solution (Alsever & Ainslie, 41 N. Y. St. J.Med. 126-35 (1941), DeGowin's Solution (DeGowin et al., 114 J.A.M.A.850-55 (1940)), Edglugate-Mg (Smith et al., 38 J. Thorac. Cardiovasc.Surg. 573-85 (1959)), Rous-Turner Solution (Rous & Turner 23 J. Exp.Med. 219-37 (1916)), other glucose mixtures, heparin, or ethylbiscoumacetate. See Hum Storage of Blood 26-160 (Acad. Press, NY, 1968).

Various procedures are known in the art and can be used to enrichcollected cord blood for HCSs. These include but are not limited toequilibrium density centrifugation, velocity sedimentation at unitgravity, immune rosetting and immune adherence, counterflow centrifugalelutriation, T lymphocyte depletion, and fluorescence-activated cellsorting, alone or in combination. See, e.g., U.S. Pat. No. 5,004,681.

Typically, collected blood is prepared for cryogenic storage by additionof cryoprotective agents such as DMSO (Lovelock & Bishop, 183 Nature1394-95 (1959); Ashwood-Smith 190 Nature 1204-05 (1961)), glycerol,polyvinylpyrrolidine (Rinfret 85 Ann. N.Y. Acad. Sci. 576-94 (1960)),polyethylene glycol (Sloviter & Ravdin 196 Nature 899-900 (1962)),albumin, dextran, sucrose, ethylene glycol, i-erythritol, D-ribitol,D-mannitol (Rowe, 3(1) Cryobiology 12-18 (1966)), D-sorbitol,i-inositol, D-lactose, choline chloride (Bender et al., 15 J. Appl.Physiol. 520-24 (1960)), amino acids (Phan & Bender, 20 Exp. Cell Res.651-54 (1960)), methanol, acetamide, glycerol monoacetate (Lovelock, 56Biochem. J. 265-70 (1954)), and inorganic salts (Phan & Bender, 104Proc. Soc. Exp. Biol. Med. (1960)). Addition of plasma (e.g., to aconcentration of 20-25%) may augment the protective effect of DMSO.

Collected blood should be cooled at a controlled rate for cryogenicstorage. Different cryoprotective agents and different cell types havedifferent optimal cooling rates. See e.g., Rapatz, 5(1) Cryobiology18-25 (1968), Rowe & Rinfret, 20 Blood 636-37 (1962); Rowe, 3(1)Cryobiology 12-18 (1966); Lewis et al., 7(1) Transfusion 17-32 (1967);Mazur 168 Science 939-49 (1970). Considerations and procedures for themanipulation, cryopreservation, and long-term storage of HSC sources areknown in the art. See e.g., U.S. Pat. No. 4,199,022; U.S. Pat. No.3,753,357; U.S. Pat. No. 4,559,298; U.S. Pat. No. 5,004,681. There arealso various devices with associated protocols for the storage of blood.U.S. Pat. No. 6,226,997; U.S. Pat. No. 7,179,643

Considerations in the thawing and reconstitution of HCS sources are alsoknown in the art. U.S. Pat. No. 7,179,643; U.S. Pat. No. 5,004,681. TheHCS source blood may also be treated to prevent clumping (see Spitzer,45 Cancer 3075-85 (1980); Stiff et al., 20 Cryobiology 17-24 (1983), andto remove toxic cryoprotective agents (US Pat. No. 5,004,681). Further,there are various approaches to determining an engrafting cell dose ofHSC transplant units. See U.S. Pat. No. 6,852,534; Kuchler Biochem.Methods in Cell Culture & Virology 18-19 (Dowden, Hutchinson & Ross,Strodsburg, Pa., 1964); 10 Methods in Medical Research 39-47 (Eisen, etal., eds., Year Book Med. Pub., Inc., Chicago, Ill., 1964).

Thus, not being limited to any particular collection, treatment, orstorage protocols, an embodiment of the present invention provides forthe addition of an HSC modulator, such as PGE2 or dmPGE2 to the neonatalblood. This may be done at collection time, or at the time ofpreparation for storage, or upon thawing and before infusion.

For example, stem cells isolated from a subject, e.g., with or withoutprior treatment of the subject with HSC modulators, may be incubated inthe presence of HSC modulators, e.g., HSC modulators such as PGE2 orthose listed in Table 1, in order to expand the number of HSCs. ExpandedHSCs may be subsequently reintroduced into the subject from which theywere obtained or may be introduced into another subject.

The HSC modulators, including PGE2 and the compounds set forth in Table1 and disclosed herein, can thus be used for, inter alia: reducing thetime to engraftment following reinfusion of stem cells in a subject;reducing the incidence of delayed primary engraftment; reducing theincidence of secondary failure of platelet production; and reducing thetime of platelet and/or neutrophil recovery following reinfusion of stemcells in a subject. These methods typically include the steps ofadministering an HSC modulator to a subject in need thereof to enhanceexpansion of the stem cell population within bone marrow and/or mobilizethe stem cells in peripheral circulation and then harvesting one or moreof the bone marrow stem cells or the stem cells in the peripheralcirculation and then transplanting the harvested stem cell back into thesubject at the appropriate time, as determined by the particular needsof the subject.

The HSC modulators, e.g., HSC modulators that cause an increase HSCnumbers, can provide a convenient single dose therapy to improve theefficiency of stem cell transplantation, to permit more aggressivetreatment of solid tumors, myeloma and lymphoma and to increase thenumber of candidates for stem cell transplantation.

The method of the invention may also be used to increase the number ofstem cells from a donor subject (including bone marrow cells or cordblood cells), whose cells are then used for rescue of a recipientsubject who has received bone marrow ablating chemotherapy orirradiation therapy.

As used herein, a subject includes anyone who is a candidate forautologous stem cell or bone marrow transplantation during the course oftreatment for malignant disease or as a component of gene therapy. Otherpossible candidates are subjects who donate stem cells or bone marrow tosubjects for allogeneic transplantation for malignant disease or genetherapy. Subjects may have undergone irradiation therapy, for example,as a treatment for malignancy of cell type other than hematopoietic.Subjects may be suffering from anemia, e.g., sickle cell anemia,thalessemia, aplastic anemia, or other deficiency of HSC derivatives.

The method of the invention thus provides the following benefits: (1)Allows transplantation to proceed in patients who would not otherwise beconsidered as candidates because of the unacceptably high risk of failedengraftment; (2) Reduces the number of aphereses required to generate aminimum acceptable harvest; (3) Reduces the incidence of primary andsecondary failure of engraftment by increasing the number HSCs availablefor transplantation; and (4) Reduces the time required for primaryengraftment by increasing the number of committed precursors of theimportant hemopoietic lineages.

The HSC modulators of the invention may have the clinical benefits instem cell transplantation of improvement of apheresis yields andimprovement of the engraftment potential of apheresed cells.

The HSC modulators of the invention, e.g., HSC modulators that cause adecrease of HSC numbers, may also be of use in treating subjectssuffering from hyperproliferative disorders of the hematopoietic system.Hyperproliferative disorders may include, but are not limited to,polycythemia vera, essential thrombocythemia, myelofibrosis with myeloidmetaplasia, and chronic myelogenous leukemia.

The compounds or agents of the present invention can be contained inpharmaceutically acceptable formulations. Such a pharmaceuticallyacceptable formulation may include a pharmaceutically acceptablecarrier(s) and/or excipient(s). As used herein, “pharmaceuticallyacceptable carrier” includes any and all solvents, dispersion media,coatings, antibacterial and anti fungal agents, isotonic and absorptiondelaying agents, and the like that are physiologically compatible. Forexample, the carrier can be suitable for injection into thecerebrospinal fluid. Excipients include pharmaceutically acceptablestabilizers. The present invention pertains to any pharmaceuticallyacceptable formulations, including synthetic or natural polymers in theform of macromolecular complexes, nanocapsules, microspheres, or beads,and lipid-based formulations including oil-in-water emulsions, micelles,mixed micelles, synthetic membrane vesicles, and resealed erythrocytes.

When the agents or compounds are delivered to a patient, they can beadministered by any suitable route, including, for example, orally(e.g., in capsules, suspensions or tablets) or by parenteraladministration. Parenteral administration can include, for example,intramuscular, intravenous, intraarticular, intraarterial, intrathecal,subcutaneous, or intraperitoneal administration. The agent can also beadministered orally, transdermally, topically, by inhalation (e.g.,intrabronchial, intranasal, oral inhalation or intranasal drops) orrectally. Administration can be local or systemic as indicated. Agentscan also be delivered using viral vectors, which are well known to thoseskilled in the art.

Both local and systemic administration are contemplated by theinvention. Desirable features of local administration include achievingeffective local concentrations of the active compound as well asavoiding adverse side effects from systemic administration of the activecompound. In a preferred embodiment, the antagonist is administeredlocally. Localized delivery techniques are described in, for example, 51J. Biomed. Mat. Res. 96-106 (2000); 100(2) J. Control Release 211-19(2004); 103(3) J. Control Release 541-63 (2005); 15(3) Vet. Clin. NorthAm. Equine Pract. 603-22 (1999); 1(1) Semin. Interv. Cardiol. 17-23(1996)

The pharmaceutically acceptable formulations can be suspended in aqueousvehicles and introduced through conventional hypodermic needles or usinginfusion pumps.

The amount of agent administered to the individual will depend on thecharacteristics of the individual, such as general health, age, sex,body weight and tolerance to drugs as well as the degree, severity andtype of rejection. The skilled artisan will be able to determineappropriate dosages depending on these and other factors.

HSC modulators within the scope of the present invention may beidentified in a variety of ways, such as the zebrafish genetic system.The zebrafish is an excellent genetic system for the study of vertebratedevelopment and diseases. See e.g., Hsia & Zon, 33(9) Exp. Hematol.1007-14 (2005); de Jong & Zon; 39 Ann. Rev. Genet. 481-501 (2005);Paffett-Lugassy & Zon, 105 Meth. Mol. Med. 171-98 (2005); Haffner &Nusslein-Volhard, 40 Int'l J. Devel. Biol. 221-27 (1996). The embryodeveloping externally is transparent and organs can be easilyvisualized. Zebrafish and mammals share many of the same gene programsin development. When zebrafish mate, they give rise to large numbers(100-200 weekly) of transparent embryos. Many embryos can be placed in arelatively small space, and there is a short generation time (about 3months). Large-scale screens have generated more than 2000 geneticmutants with specific defects that affect virtually every aspect ofembryogenesis. Driever et al., 123 Devel. 37-46 (1996); Eisen, 87 Cell969-77 (1996). Many of the blood mutants have been useful in describingkey events in hematopoeisis. Dooley & Zon, 10 Curr. Op. Genet. Devel.252-56 (2000). Zebrafish have been used to perform whole organism-basedsmall molecule screens because large numbers of the embryos can bearrayed into microtiter plates containing compounds from a chemicallibrary. For example, Peterson and colleagues tested 1,100 compounds fordevelopmental defects. Peterson et al., 97 P.N.A.S. USA 12965-69 (2000).From this screen, about 2% of the compounds were lethal, and 1% caused aspecific phenotype. For example, one compound suppressed formation ofinner ear structures called otoliths, but caused no other defects.

It is also possible to screen for chemical suppressors of mutantphenotypes. Peterson et al., 22 Nat. Biotech. 595-99 (2004); Stern etal., 1 Nat. Chem. Biol. 366-70 (2005). In one such screen, chemicalswere found to rescue the gridlock mutant, a model of congenitalcoarctation of the aorta. Peterson et al., 2004. The mechanism of thisrescue involved the induction of VEGF which corrected the angiogenesisdefect. These data demonstrate that highly potent and specific compoundscan be identified using zebrafish.

Further regarding zebrafish, a high-density genetic map has beenconstructed that includes microsatellite markers, genes, and expressedsequence tags (ESTs). Knapuk et al., 18 Nat. Genet. 338-43 (1998);Shimoda et al., 58 Genomic 219-32 (1999); Kelly et al., 10 Genome Res.558-67 (2000); Woods et al., 20 Genome Res. 1903-14 (2000). Afull-length cDNA project has also been undertaken as an extension to thezebrafish EST project. A dense RH map has been constructed andintegrated with data for the genome sequencing project at the SangerCenter. An important web resource supported by the NIH is the zebrafishinformation network (ZFIN), a focal point for the community. A stockcenter and supportive laboratory called the Zebrafish InternationalResource Center (ZIRC) also greatly helps the field. The Sanger Centeris sequencing the zebrafish genome which may be completed in 2007.

The onset of definitive hematopoiesis has been studied in a number ofvertebrate species. In seminal work in the avian species, chick-quailchimeras demonstrated that definitive hematopoietic stem cells do notarise on the yolk sac, but arise within the embryo proper.Dieterien-Lievre 33 J. Embryol. Exp. Morphol. 607-19 (1975). Similarstudies in the Xenopus embryo using diploid/triploid chimeras elucidatedthat the ventral blood island (the yolk sac equivalent) played a minorrole in adult hematopoiesis compared to the dorsal lateral plate. Kau &Turpen 131 J. Immunol. 2262-66 (1983). Based on the finding that thedorsolateral plate mesoderm contained putative hematopoietic cells thatgave rise to definitive hematopoiesis, several groups furtherinvestigated the developing aorta gonad mesonephros (AGM) region.Medvinsky et al., 364 Nature 64-67 (1993); Godin et al., 364 Nature67-70 (1993). Within this region, there are clusters of cells in theventral wall of the aorta that were originally recognized in the pig.Sabin, 9 Contrib. to Embryol. 213-62 (1920). Others have suggested thatthese clusters represent early hematopoietic stem cells that are derivedfrom “hemogenic” endothelial cells.

The process of AGM hematopoiesis is evolutionarily conserved in thevertebrate. Galloway & Zon, 53 Curr. Topics Dev. Biol. 139-58 (2003). Inmouse, the onset of stem cells occurs at 8.5 days to 9 days, just ascirculation is beginning. Hematopoietic stem cells of the AGM region atday eleven can be transplanted, however, the cells at day ten will notlead to long term engraftment. Further studies have elucidated that theaorta is polarized, and factors from the ventral and dorsal regions willmodify the behavior of cells. For instance, the dorsal region of theaorta is derived from somitic mesoderm. It is under the influence ofTGFα, BMP, and sonic hedgehog signaling. Parnanud & Dieterlen-Lievre,126 Devel. 617-27 (1999).

Cell marking studies have demonstrated that the putative HSC in the AGMhave the potential to invade the subaortic mesenchyme and also a varietyof tissues. Jaffredo et al., 125 Devel. 4575-83 (1998); Jaffredo et al.,224 Devel. Biol. 204-14 (2000). These cell marking studies used Indiaink or cells infected by retroviruses tagged with LacZ infused into thevasculature. These fate mapping experiments showed labeling ofhematopoietic cells within tissues. These studies elucidate the onset ofhematopoietic stem cells within the aorta in the vertebrate embryo

Several genes have been found to be required for AGM hematopoiesis. Thegene, runx1 (previously AML1 oncoprotein), is expressed in the aorticwall in the ventral region where the hematopoietic cells are found; thisgene function is required for AGM hematopoiesis. Cal et al., 13 Immunity423-31 (2000). The runx1 mutant mouse lacks an AGM and has defectivehematopoiesis. The defect in the runx1 mutant can be rescued by a runx1transgene driven by the Tie2 promoter, demonstrating that endothelialand hematopoietic driven expression of runx1 is sufficient to regulateAGM hematopoiesis. Miller et al., 32 Nature Genet. 645-49 (2002). In arunx1 knock-in, there are subaortic mesenchymal cells that are labeledwith LacZ, and this observation has been interpreted to mean that someof the subaortic cells may give rise to hematopoietic stem cells. Northet al., 126 Devel. 2563-75 (1999). Recent studies, have demonstratedthat the subaortic endothelial cells push through the endothelial layerand form hematopoietic clusters. Bertrand et al., 102 P.N.A.S. USA134-39 (2005); Tavian & Peault, 33 Exp. Hemat. 1062-69 (2005); Tavian &Peault, 49 Int'l J. Devel. Biol. 243-50 (2005); Tavian et al., 1044 Ann.NY Acad. Sci. 41-50 (2005).

Thus, it may be disputed whether the hemogenic endothelial cells or thesubaortic mesodermal cells are the true precursors of HSCs. Once thehematopoietic stem cells bud off the endothelial wall, they are CD45+and express the transcription factors runx1 and c-myb. The AGM cells arealso under control by notch signaling. The notch1 knock-out mouse AGMhematopoietic stem cells and runx1 and c-myb expression are absent inthe aorta region. Kumano et al., 18 Immunity 699-711 (2003);Robert-Moreno et al., 132 Devel. 1117-26 (2005). In addition, the coupTFtranscription factor also lacks AGM hematopoietic stem cells, althoughit has not been studied as thoroughly. You et al., 435 Nature 98-104(2005). Although runx1, cymb, notch, and coup appear to be important forAGM hematopoiesis, the interaction, temporal and spatial relation ofthese factors, and role of other potentially unknown factors is notknown. A better understanding of the genetic program of the onset ofhematopoiesis is clearly necessary.

A chemical genetic screen was conducted to identify novel pathways thatmodulate definitive HSC formation during zebrafish embryogenesis.FIG. 1. Genes such as runx1 and cmyb, required for HSC developmentduring mammalian hematopoiesis, are expressed in the ventral wall of thedorsal aorta in a region analogous to the mammalian AGM at thirty-sixhours post-fertilization (hpf). North et al., 16 Immunity 661-72 (2002);Mukouyama et al., 9 Curr. Biol. 833-86 (1999); Kalev-Zylinska et al.,129 Devel. 2015-30 (2002); Burns et al., 30 Exp. Hematol. 1381-89(2002). Wild-type embryos were incubated with individual compounds fromthe three-somite stage until thirty-six hpf. Probes for runx1 and cmybwere combined and utilized to detect HSCs by in situ hybridization. Themajority of chemicals, 2275 of 2357 (91.7%), failed to alter runx1/cmybexpression, while 35 (1.4%) and 47 (1.9%) led to increased or decreasedAGM HSCs, respectively.

Of the eighty-two substances that changed runx1/cmyb expression, tenaffect the prostaglandin (PG) pathway. PGs are formed from arachidonicacid by cox1, cox2, and tissue specific isomerases. At least five PGpathway compounds increased HSC gene expression (Table 1), and fivedecreased HSC gene expression (Table 2). At thirty-six hpf, runx1/cmyb+HSCs comprise a line of flattened endothelial cells and hematopoieticclusters in the aorta. Linoleic acid (10 μM), a PG precursor, increasedrunx1/cmyb+ HSCs (22 altered/30 scored) whereas celecoxib (20 μM), aselective inhibitor of cox2, decreased HSCs (26/31). The vascular markerflk1 remained relatively unchanged. Prostaglandin E2 is the maineffector prostanoid produced in the zebrafish (Grosser et al., 99P.N.A.S. USA 8418-23 (2002)), and is regulated by both cox1 and cox2.Zebrafish embryos were exposed to inhibitors of prostaglandin synthesis,as well as exogenous prostanoids. Treatment with PGE2 (25/49) resultedin stronger expression of runx1/cmyb than PGI2 (28/47) at 20 μM, whilethe isoform-selective inhibition of cox activity with SC560 (cox1, 10μM, 30/36) and NS398 (cox2, 20 μM, 35/44) as well as non-specific coxinhibitors led to decreased HSCs. These findings argue persuasively fora specific role of PGs in the formation of AGM HSCs.

TABLE 1 Example HSC modulators that increase HSCs Effect on HSCexpression # Times (# embryos altered/ Compound Identified # embryosscored) Mead Acid 2 Increase (24/32) Linoleic Acid 1 Increase (22/30)13(S)-HODE 1 Increase (15/25) Ly-171883 1 Increase (17/26)Epoxyeicosatrienoic Acid 1 Increase (17/25) PG pathway compoundsidentified as modulating runx1/cmyb⁺ HSCs are listed in column one.Column two denotes the frequency at which a particular compound wasidentified. The third column shows the effect of the compound on HSCgene expression (# embryos altered/# embryos scored).

TABLE 2 Example HSC modulators that decrease HSCs Effect on HSCexpression # Times (# embryos altered/ Compound Identified # embryosscored) Celecoxib 2 Decrease (26/31) Fenbufen 1 Decrease (20/26)Prosteglandin J2 1 Decrease (12/22) Suxibuzone 1 Decrease (16/30)Sulindac 1 Decrease (18/31) PG pathway compounds identified asmodulating runx1/cmyb⁺ HSCs are listed in column one. Column two denotesthe frequency at which a particular compound was identified. The thirdcolumn shows the effect of the compound on HSC gene expression (#embryos altered/# embryos scored).

Additional HSC prostaglandin pathway modifiers were identified using thezebrafish screening techniques described herein such as those shown inTable 3:

TABLE 3 Example prostaglandin pathway modifiers HSC Inhibitors HSCEnhancers Indomethacin dmPGE2 SC560 PGE2 NS398 PGI2 AspirinEicosatrienoic Acid Ibuprofen ONO-259 Naproxen Cay10397 AristolochicAcid AH6809 (EP½ antag) AH23848 (EP4 antag)

The expression of cox1 in the vasculature was described previously;knock-down of cox1 activity inhibited the development of the endothelialboundary between the aorta and vein. Cha et al., 282 Devel. Biol. 274-83(2005). As HSCs arise from a hemogenic endothelial cell population, lossof cox1 function would impact HSC development. By in situ hybridization,cox2 was diffusely expressed in the tail region encompassing the AGM atthirty-six hpf. In FACS-isolated blood and endothelial cell populations,both cox1 and cox2 were found to be upregulated during the switch fromprimitive to definitive hematopoiesis. High levels of cox1 expressionwere detected in both lmo2+ endothelial cells and in CD41+ HSCs, whilecox2 was only upregulated in the HSC fraction (FIG. 2, Panel A). Theseresults suggest that cox1 and cox2 participate in the induction of AGMHSCs through regulation of stem cell niche, as well as in the HSCitself.

Linoelic Acid and Mead Acid can act as substrates for prostaglandinproduction and were isolated in the screen as agents that upregulatedHSC formation. To determine which prostaglandin was mediating theincrease in HSCs in the AGM, zebrafish were exposed to exogenouspurified prostaglandins from three somites to 36 hpf and stained asdescribed previously. In the zebrafish, the major physiologically activeprostaglandins are PGE2, PGI2 and PGF2. Pini et al., 25 Arterioscler.Thromb. Vasc. Biol. 315-20 (2005); Grosser et al., 2002. Each of thesewas tested for their effect on AGM HSCs. Both PGE2 and PGI2, were foundto increase moderately the numbers of Runx1+Cmyb+ cells in the AGM,while PGF2 had no effect. Due to the tight regulation of prostaglandinproduction and destruction in vivo, a slowly metabolized version of PGE2was also examined.

A long-acting derivative, 16,16-dimethyl-PGE2 (dmPGE2, 10 μM) caused anincrease in runx1/cmyb+ AGM HSCs in 78% of embryos examined (97/124).AGM HSCs were inhibited by indomethacin (10 μM) treatment in 90% ofembryos analyzed (92/102). PGE2 was the most abundant PG measured bymass spectrometry in 36 hpf embryos (18+/−6 pg/50 embryos; n=4), andindomethacin treatment depressed PGE2 formation below detectable levels(<2 pg/50 embryos; n=3) 7. Treatment with dmPGE2 had minimal effects onthe vasculature by flk1 staining; indomethacin slightly altered theintersomitic vessels in 30% of embryos examined (15/49). Transgeniccmyb:GFP zebrafish with green fluorescent HSCs and myeloid progenitorcells were crossed to lmo2:dsRed fish that have red fluorescentendothelial cells and HSCs to visualize the effects of chemical exposurein vivo. At 36 hpf, live embryos imaged by confocal microscopy exhibitedsignificantly decreased numbers of HSCs along the floor of the aortafollowing indomethacin treatment, and significantly increased HSCs afterdmPGE2 exposure. FIG. 3. This indicates that PG affects the total numberof HSCs formed along the dorsal wall of the aorta; induction of HSCs ataberrant locations is not evident. By qPCR runx1 expression was 3-foldenhanced after addition of dmPGE2, while indomethacin caused asignificant 50% reduction in runx1 expression; significant alterationsin the expression of cmyb were also observed (FIG. 2, Panel B).

To confirm the requirement of PGE2 activity, low-dose (40 μM) morpholinooligonucleotides (MO) was used to knock down expression of cox1 and cox2; low dose inhibition of cox1 activity allowed embryos to proceedthrough gastrulation, while mimicking cox-dependent developmentaldefects. Grosser et al., (2002). MO inhibition of cox decreased AGM HSCs(cox1 54/74; cox2 60/71). Mass spectroscopy analysis demonstrated PGE2was below detectable levels in these embryos, consistent withMO-mediated suppression of endogenous prostaglandin synthesis (n=4). Theeffects on HSCs were reversed by incubation of MO-injected embryos with10 μM dmPGE2 (cox1/dmPGE2 29/52 rescued; cox2/dmPGE2 43/60). MOknockdown of PGE2 synthase caused a reduction of HSCs (35/50), which wasrescued by dmPGE2 addition (25/45), indicating that signaling throughPGE2 was sufficient to modulate HSC formation. PGE2 signals throughseveral receptors, EP1-4, all of which are present in the zebrafishgenome. Cha et al., 20 Genet. Devel. 77-86 (2002). MO knockdown of theEP2 and EP4 receptors resulted in diminished runx1/cmyb expression (EP239/63; EP4 44/67) that was not reversed by exposure to exogenous dmPGE2.Analysis by qPCR demonstrated that EP2 and EP4 were present in bothCD41+ HSC and CD41-non-stem cell FACS sorted cell populations at 36 hpf.These experiments confirm that PGE2-mediated signaling regulates theformation of HSCs in the AGM region.

To further explore the interactions between prostaglandins and HSCproduction, numerous prostaglandin derivatives were screened using thezebrafish embryo technnique described herein. In general, the assaysindicated that derivatives that enhanced stability of PGE2 increasedHSCs. Those for which no enhancement was observed relative to controlstended to be compounds that bound preferentially to the receptors thatwere not active in HSCs. The effects of these compounds on HSC numbersare indicated in Table 4:

TABLE 4 Prostaglandin derivatives effecting HSC production

PGE2

 

16,16-dimethyl PGE2 20-hydroxy PGE2

 

19(R)-hydroxy PGE2

 

16,16-dimethyl PGE2 p-(p-acetamidobenzamido) phenyl ester

11-deoxy-16,16-dimethyl PGE2

 

9-deoxy-9-methylene-16,16-dimethyl PGE2

 

9-deoxy-9-methylene PGE2 9-keto Fluprostenol

Butaprost

Sulprostone toxic 5-trans PGE2 17-phenyl trinor PGE2

PGE2 serinol amide

 

PGE2 methyl ester

 

 

16-phenyl tetranor PGE2

 

15(S)-15-methyl PGE2

 

15(R)-15-methyl PGE2 8-iso-15-keto PGE2 8-iso PGE2 isopropyl ester

 indicates relative potency to increase HSC production. No arrowindicates insignificant HSC enhancement relative to control.

To examine the role of PGE2 in HSC homeostasis in adult zebrafish, akidney marrow (KM) irradiation recovery assay was performed. Burns etal., 19 Genes & Devel. 2331-42 (2005). Wild-type fish were sublethallyirradiated, exposed to dmPGE2, and evaluated for kinetics of KM recoveryby FACS 11 (FIG. 4A). The rate of hematopoietic reconstitution of the KMwas significantly enhanced in fish exposed to 50 μM dmPGE2 compared toDMSO-exposed controls (FIG. 4A, B). The elevation in percentage ofprogenitors preceded recovery of the myeloid and lymphoid populations,respectively. The expression levels of stem, progenitor and endothelialcell markers by qPCR on PGE2-treated KM at day three post-irradiationshowed significant upregulation of runx1 and lmo2 (FIG. 5). Inhibitionof cox activity by non-selective and selective inhibitors significantlydecreased KM recovery and affected overall survival (FIG. 5). Ourresults indicate that PGE2 plays an important role in KM homeostasis.

The effects of the prostaglandin pathway on mammalian HSC and progenitorpopulations were also evaluated. Addition of dmPGE2 to ES cells duringembryoid body expansion increased hematopoietic colonies number on anOP9 stromal cell layer and in methylcellulose colony-forming assays(FIG. 6A, B). Nakano et al., 272 Sci. 722-24 (2002). OP9, definitiveerythroid (dE) and granulocyte/monocyte (GM) colonies increased in adose-dependent manner after exposure to 10 μM (GM p=0.005) and 20 μM(OP9 p=0.047; dE p=0.04; GM p=0.007) dmPGE2. The number of multipotentgranulocyte/erythrocyte/monocyte/macrophage (GEMM) colonies was enhanced2.9-fold following dmPGE2 treatment (10 μM: p=0.017; 20 μM: p=0.016). At100 μM, dmPGE2 was toxic to ES cells. qPCR was performed to determine ifPG pathway components were present in ES cells: Cox1, Cox2, PGE2synthase, and PGE receptors 1-4 were present at all stages examined.Indomethacin inhibited colony growth at 20 μM (OP9 p=0.047) and 100 μM(GM p=0.024) (FIG. 6A, B); the inhibitory effects were rescued byexogenous dmPGE2 in both colony-forming assays (FIG. 7A, B). These datasuggest that the role of the prostaglandin pathway in hematopoiesis isconserved between zebrafish and mammals.

Alternatively, the expansion of hematopoietic or endothelial cells inthe AGM (aorta-gonad-mesonephros) region may be studied by mating mice,then dosing newly pregnant females with PGE2 in their drinking waterstarting at day 8.5 of embryonic development. PGE2 levels may have aneffect on implantation of murine embryos; waiting until day 8.5 to begintreatment allows implantation to proceed, yet still provides time forthe drug to affect the stem cell population that can be found in the AGMregion starting at day 10.5. Pregnant females are sacrificed with CO2 atday 11.5 of embryonic development and embryos are isolated from theuterus and fixed with paraformaldehyde. Fixed embryos may be processedfor whole mount in situ hybridization for markers of HSCs, such asRunx1, c-myb or Scat, or subjected to immunohistochemistry withantibodies to HSCs to find evidence of an expanded stem cell population.Different doses, e.g., 10(−1), 10(−3) and 10(−5) micrograms/g bodyweight, may be used. Three pregnant female mice may be used for eachdose noted above, and for an unexposed control variable. The effectivedose is then used in transplantation experiments involving cellsdissected from the AGM region of embryos.

Expansion of CFU-S and Long-term Repopulating HSCs may be studied inmice as well. The single dose of PGE2 found to expand potential stemcells in the AGM region may be fed to pregnant females followingimplantation (approx E8.5) in the drinking water. Control females aretreated in parallel. Pregnant females are euthanized at 11.5 dpc. Theembryos are collected from the uterus, the AGM region isolated bymicrodissection and AGM cells prepared for transplantation. Acombination of one embryo equivalent of experimental and/or controlcells will be injected into the tail vein of irradiated recipient mice,where they will home to the spleen (short term) and bone marrow (longterm). The contribution of experimental cells versus control cells maybe analyzed at twelve days post transplant by a standard CFU-S assay forspleen colony number of sacrificed recipient mice, or by flow cytometryof bone marrow at one month post-transplantation to determinecompetitive long-term HSC repopulation.

Because the development of the cardiovascular system is intimatelylinked to the production of hematopoietic stem cells duringembryogenesis, the effect of blood pressure on PGE2 signaling and theinduction of AGM HSCs may be relevant. The most conserved site forhematopoiesis in any vertebrate is the ventral wall of the aorta. Thecells in the aorta arise at thirty hours of development in the zebrafishand develop there until about forty-six hours when they entercirculation or invade tissues. AGM HSC production may be timed to occurafter the first heartbeat and when blood pressure within the vasculaturereaches a critical level. In the zebrafish, the first heartbeat occursat twenty-three hours. At this time, the heartbeat is slow and thecontraction of the heart is relatively weak. At thirty hours, robustcirculation is established. The cue to make AGM stem cells may be analteration in blood pressure. Several chemicals identified in zebrafishscreening regulate blood pressure and cardiac contractility. Forexample, the chemical hydralazine, a commonly used antihypertensive, isknown to increase prostaglandin E2 expression. In situ analysis ofembryos exposed to hydralazine demonstrates very few chances inangiogenesis, but a great increase in blood stem cell number. Inaddition, the drug strophanthidin, a cardiac glycoside, increasescontractility of the heart and also increases AGM stem cells.Furthermore, the beta-blocker, atenolol, leads to vasodilation and alsoleads to a heightened production of AGM stem cells. Chemicals thatperturb heart beat, such as BDM and epinephrine, as well as the silentheart mutant may alter the production of AGM stem cells, and mayestablish if circulation is necessary for AGM production. To furtherestablish the relationship between blood pressure and the prostaglandinpathway, hydralazine, strophanthidin, and atenolol may be incubated withthe zebrafish in the presence of COX2 inhibitors. Similar studies can bedone with the COX2 morpholino to determine if they are able to block theactivation of stem cells mediated by hydralazine.

To explore potential in vivo effects, murine whole bone marrow (WBM) wasexposed ex vivo to dmPGE2 (1 μM/106 cells) and irradiated recipientswere transplanted with 6×10⁴ treated WBM cells. The number of CFU-S12was increased three-fold (p<0.0001) in recipients of dmPGE2-treated WBM(FIG. 8 b, FIG. 9A, Table 6-Table 8); similarly, more mature CFU-S8colonies were also enhanced (FIG. 9A, Table 5). To assess the endogenousPGE2 requirement, WBM cells were incubated ex vivo with indomethacin (1μM/106 cells). After transplantation of 1×10⁵ cells, a 70% decrease(p=0.0002) in the number of CFU-S12 was observed in recipients ofindomethacin-treated cells (FIG. 8C, FIG. 9C, Table 4-Table 6); similarresults were seen with specific cox1 and cox2 inhibition (FIG. 9K, L).These results suggest that PGE2 treatment not only enhanceshematopoietic stem cell formation, but is required for CFU-S activity.

TABLE 5 Effect of dmPGE2 on CFU-S₁₂ # Cells CFU-S¹² (n + 10) Ex vivoMurine Cell Trans- Weight mg Colony Treatment Population planted Ave(SD) Number EtOH Whole Marrow 6000 41.9 (15.8) 5.8 (2.6) dmPGE2 WholeMarrow 6000 85.4 (16.5) 15.2 (2.2)  EtOH Whole Marrow 100000 71.8 (18.1)8.8 (2.1) Indomethacin Whole Marrow 100000 32.7 (8.7)  2.5 (1.4) EtOHKit+Sca+Lin− 100 25.1 (5.9)  3.0 (1.4) dmPGE2 Kit+Sca+Lin− 100 47.7(5.6)  6.2 (1.2) EtOH Kit+Sca+Lin− 300 46.1 (5.6)  5.0 (1.1) dmPGE2Kit+Sca+Lin− 300 88.2 (14.8) 11.0 (1.7)  Spleen weight and CFU-Sactivity was assessed at day twelve in irradiated recipients injectedwith either WBM or ckit+sca1+lineage− FACS sorted cells treated withEtOH, dmPGE2 or indomethacin (1 μM/10⁶ cells).

TABLE 6 Effect of dmPGE2 on radio-protective competitive BMrepopulation. 6 wk CD45.1 Engraftment CD45.2 CD45.1/2 Animals RecipientsEx vivo CD45.1 Test Competitor with >5% Mean % CD45.1 Analyzed TreatmentCell Dose Cell Dose CD45.1 chimerism (±SD) Total EtOH 15000 200000 3 4.0± 7.8 10 50000 200000 4 5.8 ± 5.7 8 200000 200000 9 32.5 ± 20.7 102000000 200000 9 52.4 ± 34.8 9 dmPGE2 15000 200000 7 16.9 ± 19.5 1050000 200000 8 22.7 ± 24.2 10 200000 200000 10 41.9 ± 17.2 10 2000000200000 10 85.1 ± 3.1  10 WBM (CD45.1) was treated ex vivo with EtOHvehicle or dmPGE2 and transplanted into sublethally irradiatedrecipients (CD45.2) with a fixed number of (CD45.1/CD45.2) competitorcells at the ratios shown in columns 2 and 3. Column 4 illustrates thenumber of animals with more than 5% CD45.1 chimerism at six weeks, andcolumn 5 demonstrates the mean percentage of chimerism. The last columnindicates the number of CD45.2 recipients analyzed.

TABLE 7 Effect of dmPGE2 on radio-protective competitive BMrepopulation. 12 wk CD45.1 Engraftment CD45.2 CD45.1/2 AnimalsRecipients Ex vivo CD45.1 Test Competitor with >5% Mean % CD45.1Analyzed Treatment Cell Dose Cell Dose CD45.1 chimerism (±SD) Total EtOH15000 200000 2 1.9 ± 2.9 9 50000 200000 3 5.4 ± 4.4 8 200000 200000 1046.9 ± 22.9 10 2000000 200000 10 82.8 ± 14.1 9 dmPGE2 15000 200000 515.1 ± 22.2 10 50000 200000 8 18.1 ± 22.2 10 200000 200000 10 40.8 ±28.7 10 2000000 200000 10 87.8 ± 4.0  10 WBM (CD45.1) was treated exvivo with EtOH vehicle or dmPGE2 and transplanted into sublethallyirradiated recipients (CD45.2) with a fixed number of (CD45.1/CD45.2)competitor cells at the ratios shown in columns 2 and 3. Column 4illustrates the number of animals with more than 5% CD45.1 chimerism attwelve weeks, and column 5 demonstrates the mean percentage ofchimerism. The last column indicates the number of CD45.2 recipientsanalyzed.

TABLE 8 Effect of dmPGE2 on radio-protective competitive BMrepopulation. 24 wk CD45.1 Engraftment CD45.2 CD45.1/2 AnimalsRecipients Ex vivo CD45.1 Test Competitor with >5% Mean % CD45.1Analyzed Treatment Cell Dose Cell Dose CD45.1 chimerism (±SD) Total EtOH15000 200000 1 1.9 ± 2.5 9 50000 200000 2 4.7 ± 4.2 7 200000 200000 1051.18 ± 26.3  10 2000000 200000 9 81.7 ± 24.4 9 dmPGE2 15000 200000 410.2 ± 10.3 9 50000 200000 7 14.3 ± 16.6 10 200000 200000 10 39.1 ± 31.010 2000000 200000 10 90.7 ± 4.0  10 WBM (CD45.1) was treated ex vivowith EtOH vehicle or dmPGE2 and transplanted into sublethally irradiatedrecipients (CD45.2) with a fixed number of (CD45.1/CD45.2) competitorcells at the ratios shown in columns 2 and 3. Column 4 illustrates thenumber of animals with more than 5% CD45.1 chimerism at twenty-fourweeks, and column 5 demonstrates the mean percentage of chimerism. Thelast column indicates the number of CD45.2 recipients analyzed.

The PG pathway components are present in both stromal cell and HSCpopulations in mice and humans (Princeton Stem Cell and Stromal celldatabases). Ivanova et al., 298 Sci. 601-04 (2002); Nakano et al., 101Blood 383-89 (2003). Cox1, Cox2, PGE2-synthase and receptors EP2 and EP4are present in fetal liver HSCs and in BM HSC after 5-fluorouracil (5FU)injury, suggesting PGE2 signaling is utilized by HSCs. Venezia et al.,PLoS Biol 2, e301 (2004). To determine if the increase in CFU-S numberis due to a direct effect of PGE2 on the stem cell population,FACS-isolated ckit+scal+lineage-(KSL) BM cells were exposed to dmPGE2and transplanted at 100 or 300 cells per irradiated recipient. Bothsplenic weight (FIG. 9D) and CFU-S12 were significantly increased inrecipients of dmPGE2-treated cells (FIG. 9D, Table 6-Table 8). Theseresults indicate that dmPGE2 can lead to cell autonomous activation ofHSCs and immature progenitors.

To determine whether dmPGE2 exposure can enhance HSC reconstitution,limiting dilution competitive repopulation analysis was conducted. Zhang& Lodish, 103 Blood 2513-21 (2004). WBM (CD45.1) exposed to dmPGE2 exvivo was mixed independently at varying doses with a fixed number ofuntreated competitor cells (CD45.1/CD45.2) and injected into congenicrecipient mice (CD45.2). Peripheral blood was obtained at six, twelve,and twenty-four weeks post-transplantation and examined by FACS todetermine the contribution of treated-test cells to hematopoieticrepopulation (FIGS. 9E-9J). Positive reconsitution was defined as testcell multi-lineage chimerism >5% (FIGS. 9F, H, I). A significantincrease in the number of repopulating cells as determined by Poissonstatistical analysis was seen in dmPGE2-treated BM (FIG. 8E, FIGS. 9G,9J). At six weeks, the calculated frequency of engrafting cells per 106WBM cells was enhanced 3.3-fold (p=0.005) in the recipients ofdmPGE2-treated WBM, and the frequency of short-term repopulating HSCswas 4-fold (p=0.002) higher at twelve weeks post-transplant (FIG. 8E,8F, FIG. 9G). At twenty-four weeks, the frequency of long-termrepopulating HSCs was 2.3-fold enhanced (p=0.05) in recipients ofdmPGE2-treated cells (FIG. 8F, FIG. 9J). At both the twelve- andtwenty-four-week analyses, reconstitution in all recipients wasmultilineage, indicating that transient dmPGE2 treatment increased thefrequency of repopulating HSCs in the mouse without impairingdifferentiative capacity. No decline in the contribution ofdmPGE2-treated HSCs to hematopoiesis was observed. To determine whetherdmPGE2 treatment enhanced homing to the BM niche, WBM was labeled with avital dye, CDFA, then exposed to dmPGE2 and transplanted. At twelvehours post-transplantation, there was no significant difference inhoming between the control and dmPGE2-treated cells (p=0.83).

In an effort to more precisely characterize the requirement of theprostaglandin pathway in stem cell production, several additionalcommercially available cyclooxygenase (COX) inhibitors were utilized.General COX inhibitors indomethican, naproxen, ibuprofen, and asprin, aswell as the Cox2 specific inhibitor NS-398, were all tested for effectson AGM HSCs via the assay described above. Each Cox1 or Cox2 chemicalinhibitor reduced stem cells in the aorta. Cox is responsible forprocessing PG's by altering arachadonic acid. Vasculogenesis and aortaspecification remained intact in treated embryos as seen by ephrinB2 andFlk1 staining, however some aspects of angiogenesis, particularly themorphology of the inter-somitic blood vessels, were perturbed by some ofthe chemicals. Morpholino antisense oligonucleotides for COX1 and COX2were also injected individually into zebrafish embryos to confirm thatthe reduction of stem cells in the aorta was due to Cox inhibition.Runx1+Cmyb+ cells were reduced in AGM region with either morpholino. Asreported previously, very high concentrations of the Cox1 MO causeddefects in the specification of the aorta and vein, while the cox2morpholino caused a gastrulation arrest at high concentrations. Cha etal., 20 Genes & Devel. 77-86 (2006); Cha et al., 282 Devel. Biol. 274-83(2005). The reduction in HSCs was observed at lower concentrations ofeither MO, and the vessel structures in the tail were not severelyaltered. Additionally, fli1 GFP transgenic zebrafish that preciselydelineate the vasculature were used to evaluate the effect of themorpholinos and chemicals on angiogenesis. Inhybridization of Cox 1 orCox2 does not affect development of the aorta by chemicals ormorpholinos. Intersomitic blood vessels are altered by some treatments.

Prostaglandin E2 is the major prostaglandin that is made duringzebrafish embryogenesis and regulates vascular tissues. Pini et al., 25Arterioscler Thromb Vasc Biol. 315-20 (2005); Grosser et al., 99P.N.A.S. USA 8418-23 (2002). Precisely which prostaglandins are effectedby both chemical and/or morpholino inhibition of prostaglandin pathwaycomponents may be analyzed by mass spectroscopy analysis. Similarly,mass spectroscopry may confirm E2 induction following exposure toprostaglandin pathway substrates such as lineolic acid or mead acid. Theanalysis of the role of PGE2 in the formation of AGM HSCs logicallyleads to analysis of which receptors are active in propagatingprostaglandin signaling to downstream effectors. Four PGE2 receptorshave been identified in the zebrafish. Specific agonists and antagonistsof the PGE receptors assist in this identification. Additionally thespecific receptors that are mediating HSC induction can be studied byfunctional knockdown using morpholinos as described earlier. Theexpression of each of the prostaglandin receptors, as well as bothcyclooxygenases may studied by in situ hybridization to evaluate thelocalization of these gene products throughout development, particularlyfocusing on the AGM region.

The present invention demonstrates that PGE2 enhances the number ofhematopoietic stem cells and multipotent progenitors in two vertebratespecies, zebrafish and mice. Prior studies have documented thatunmodified PGE2 can affect blood cell maturation in the mouse (Boer etal., 100 Blood 467-73 (2002); Rocca et al., 99 P.N.A.S. USA 7634-39(2002)), and the stimulation of cell cycle in CFU-S8 progenitors (Feher& Gidali, 247 Nature 550-551 (1974)); the effects of PG-mediated cellsignaling on HSCs have not been examined previously, however. cox1 andcox2 appear to have distinct functions in AGM HSC formation: cox1 isimportant in the formation of the hematopoietic niche, particularly thehemogenic endothelium, while cox2 is likely involved in the self-renewaland proliferation of HSCs themselves. Conversely, homozygous Cox1 orCox2 knockout mice are viable with no apparent defects in HSC formation(Langenbach et al., 58 Biochem. Pharmacol. 1237-46 (1999)); this isbelieved to be due to maternal and sibling contribution of PGE2. Cha etal., 282 Devel. Biol. 274-83 (2005); Langenbach et al., 83 Cell 483-92(1995).

Significantly, analyses of Cox2−/− mice demonstrated alterations inhematocrit levels and an inability to recover from 5-FU induced BMinjury (Lorenz et al., 27 Exp. Hematol. 1494-502 (1999); these findingsimply the presence of HSC defects in adult Cox2−/− mice compatible withour proposed role for PG in HSC homeostasis. To clarify the roles ofCox1 and Cox2 in regulating HSC homeostasis in the adult, we performed aCFUS12 (FIG. 9 k,l) and 5-FU bone marrow recovery assay using selectivechemical inhibitors of either cox1 (SC560) or cox2 (NS398). Inhibitionof either enzyme was found to significantly alter CFUS activity, as wellas the recovery of peripheral blood and BM WBC numbers (FIG. 9 m,n)compared to controls. Additionally, administration of dmPGE2 following5FU treatment significantly enhanced BM recovery. Together, these datasuggest that both Cox1 and Cox2 maintain a role in regulating HSChomeostasis in the adult mouse, as in the zebrafish, and that PGE2 isthe mediator of this HSC regulation.

Patients undergoing BM transplantation display increased endogenous PGE2levels. Cayeux et al., 12 Bone Marrow Transplant 603-08 (1993). Althoughcox inhibitors are not generally given post transplant because ofplatelet inhibition, our studies raised the possibility thatadministration of such agents following human BM transplantation mightimpair HSC engraftment. PGE2 and its analogues have been administeredsafely to humans. Talosi et al., 32 J. Perinat. Med. 368-74 (2004);Thanopoulos et al., 146 Eur. J. Pediatrics 279-82 (1987). These may beuseful for ex vivo or in vivo expansion of HSCs. The concentration ofdmPGE2 used to expand murine HSCs falls within the physiological rangeof PGE2 in human serum. Hertelendy et al., 3 Prostaglandins 223-37(1973). The present disclosure illustrates that PGE2 functions as apotent regulator of HSCs in vertebrates, and may prove useful intreating patients with bone marrow failure or following transplantation.

The study of hematopoiesis in zebrafish has previously focused on thefirst wave of hematopoiesis, termed primitive, and the derivation ofdefinitive hematopoietic stem cells in the aorta, gonads and mesonephros(AGM) region of the zebrafish embryo. Little is known about theproduction of AGM stem cells in vertebrates, but both runx1 and notch1have been shown to be required for AGM HSC formation. There is also agenetic relationship whereby notch regulates runx1. A large scalechemical genetic screen for effectors of stem cell induction using alibrary of about 2500 compounds with known action indicated thatchemicals that led to the production of prostaglandin (PG)E2 caused anincrease in stem cell number, whereas chemicals that prevented PGE2synthesis led to a reduction of stem cells. Other chemicals such asvasodilators and vasoconstrictors were also found to alter stem cellnumber, establishing a hypothesis that vascular tone duringembryogenesis is a trigger for stem cell production. Members of the Wntsignaling pathway have been hypothesized to regulate hematopoietic stemcell numbers, although to date these studies have exclusively examinedadult bone marrow homeostasis. The role of Wnt signaling in embryonicAGM production to identify potential genetic interactions with thenotch-runx pathway, or with the prostaglandins, is investigated. Todefine additional genes that participate in AGM stem cell formation, alarge-scale screen for mutants with defects in AGM production continues.At least twelve mutants have been isolated. The genes and pathwaysidentified may have a significant impact on our understanding of basicstem cell biology, and could lead to new therapies for diseases such assickle cell anemia, thalessemia, and aplastic anemia.

Approaches to characterizing the signaling pathways involved indefinitive hematopoietic stem cell derivation during embryogenesis,using the zebrafish as a model, include evaluating the hypothesis thatprostaglandins regulate AGM stem cell production using mutants,morphants, transgenics and chemicals and examining the role of the wntpathway in the formation of AGM HSCs and investigate potentialinteractions with other signaling pathways known to be active in the AGMregion. Zebrafish genetics may be used to define new pathways involvedin AGM HSC formation during embryogenesis and allow for large-scalemutagenesis screens for defects in definitive hematopoiesis inzebrafish. This allows for the isolation and characterizion of some ofthe mutated genes responsible for normal AGM HSC production.

Work in defining new pathways regulating the production of embryonichematopoiesis has shed light on the CDX-HOX Pathway. It was discoveredthat the defective gene responsible for the decreased number of HSCs inthe mutant zebrafish kugelig. Davidson et al., 425 Nature 300-06 (2003).The kgg mutant has a deficit of SCL+ hematopoietic stem cells duringearly embryogenesis and lacks expression of the progenitor markers,GATA-1 and runx1. The vasculature in mutant embryos forms normally, butvery few red cells circulate in the vasculature. The mutated geneencoded CDX4, a member of the caudal family. Mammals have three CDXgenes including CDX1, 2, and 4. Caudal genes are known to act byregulating the HOX genes. The posterior HOX genes showed decreasedexpression in kgg mutants. It has been established that HOX genes actdownstream of CDX4 in the development of blood. Overexpression of hoxb7or hoxa9 led to a robust rescue of the hematopoietic defect in kggmutants. To evaluate whether CDX4 is sufficient to specify thehematopoietic stem fate during embryogenesis, CDX4 mRNA was injectedinto zebrafish embryos. A number of SCL positive cells were found inregions of the embryo that normally would not form blood. The fact thatcdx4 is sufficient to induce ectopic blood stem cells allows this workto translate into the mammalian system.

Despite the significant in vitro blood-forming potential of murineembryonic stem cells (ESCs), deriving hematopoietic stem cells (HSCs)that can reconstitute irradiated mice has proven to be challenging.Researchers have successfully engrafted lethally irradiated adult micewith ESCs engineered to ectopically express hoxB4. Kyba et al., 109 Cell29-37 (2002). Blood reconstitution showed a myeloid predominance, likelydue to an inability to fully pattern the adult HSC from these embryonicpopulations. Co-expression of CDX4 and hoxb4 promotes robust expansionof hematopoietic blasts on supportive OP9 stromal cultures. Wheninjected intravenously into lethally-irradiated mice, these cellpopulations provide robust radio-protection, and reconstitute high-levellymphoid-myeloid donor chimerism. Wang et al., 102 P.N.A.S.USA 1981-86(2005).

To explore pathways that could be downstream of the cdx-hox pathway, amicroarray analysis was used to identify differentially expressed genesin kgg mutants and wild-type embryos. Raldh2, an enzyme required forretinoic acid (RA) production, is overexpressed in kgg mutants duringthe early stages of blood formation. Perz-Edwards et al., 229 Devel.Biol. 89-101 (2001); Begemann et al., 128 Devel. 3081-94 (2001). Thisdata led to the hypothesize that RA may act to suppress blood formationand that the CDX-HOX pathway functions to limit RA production, therebypermitting blood formation to occur. In other words, the cdx-hox pathwaycontrols retinoic acid signaling.

To test this, wild-type zebrafish embryos were treated with RA and,indeed, they became severely anemic. Treating kgg embryos with DEAB(Perz-Edwards, 2001), a chemical that blocks raldh2 activity, restoredhematopoiesis in kgg mutants. Treatment with DEAB failed to rescueexpression of hoxa9a, indicating that RA acts downstream of the hoxgenes. DEAB also induced an expansion of erythroid cells in wild-typeembryos. DEAB and RA also affected the formation of mouse hematopoieticprogenitors arising from ES cell-derived embryoid bodies (EBs). Additionof DEAB to EBs between days two to three of development resulted in afive-eight fold increase in ‘primitive’ erythroid colonies (CFU-Ep),analogous to results in zebrafish. Similar stimulation of primitive yolksac erythroid cells were seen with DEAB. In contrast, RA treatmentcaused a general inhibition in the growth of all colony types. Takentogether, these results suggest a new model in which suppression of RAby the CDX-HOX pathway is necessary for yolk sac hematopoiesis to occur.See also Davidson et al., 425 Nature 300-06 (2003); Davidson & Zon,292(2) Devel. Biol. 506-18 (2006).

An additional gene identified is moonshine, a gene that is required fornormal primitive and definitive erythropoiesis. The gene mutated isTif1γ, a putative regulator of chromatin. Ransom et al., 2 PloS 1188-96(2004). This factor contains a PHD finger, bromo domain, ring finger,and recently has been tied to BMP signaling through an interaction withSMAD2 and SMAD437. Dupont et al., 121 Cell 87-99 (2005). The role ofthis factor in hematopoiesis may be determined using suppressor enhancerscreens.

An additional mutant has been designated bloodless. This gene isrequired for both primitive hematopoiesis and AGM hematopoiesis,although definitive hematopoiesis recovers. The bloodless phenotypeappears to be non-cell autonomous and yet bloodless controls SCL andGATA1 expression. There is difficulty in mapping this mutant gene. Liaoet al., 129 Devel. 649-59 (2002).

Work elucidating mechanism of erythroid to myeloid fate switch showingthat GATA1 is required for suppression of the myeloid lineage. Gallowayet al., 8(1) Devel. Cell 109-16 (2005). More specifically, investigatinga GATA1 deficient zebrafish mutant, known as vlad tepes, and revealedthat the entire blood island transformed to the myeloid fate. Thisinteresting cell fate change illustrates that GATA1 and PU.1 antagonizeeach other's activity. They may form form a complex that regulates themyeloid and erythroid programs. Further work demonstrated thatknock-down of PU.1 changed myeloid cell progenitors into erythroidcells.39 Rhose et al., 8 Devel. Cell 97-108 (2005). This study providesa rational for plasticity within the hematopoietic system. Studying thedependency of target gene expression and of erythroid cells of GATA1 andGATA2 has shown that most genes are absolutely dependent on GATA1, yetsome genes require both GATA1 and GATA2 for full expression. Severalnovel genes have been found that are absolutely GATA independent.

Characterization of SCL deficient morphants indicated that this SCL MOphenotype was very similar to that of the SCL knock-out in mammalianbiology. SCL is required for the early hematopoietic cells to develop.Abnormal regulation of SCL is evident in both the cloche and spadetailmutants that are deficient in normal hematopoiesis. Dooley et al.,277(2) Devel. Biol. 522-36 (2005).

In an effort to understand blood island development, researchersisolated the LMO2 promoter and demonstrated that the proximal 163 basepairs of promoter are sufficient to induce GFP expression in thedeveloping blood island as well as the vasculature. These transgenicfish lines have been invaluable for transplantation experiments. BothDsRed as well as GFP have been linked to the LMO2 promoter, allowing theconstruction of double transgenic lines. These LMO2 positive cells ofthe primitive lineage do not confer long-term reconstitution intransplantation models of early embryos or in adults. Zhu et al., 281(2)Devel. Biol. 256-269 (2005); Mead et al., 128 Devel. 2301-08 (2001);Oates et al., 98 Blood 1792-1801 (2001); Pratt et al., 11 PhysiologicalGenomics 91-98 (2002); Huber et al., 11 Current Biology 1456-61 (2001).

A major goal was to develop hematopoietic cell transplantation for thezebrafish system. Hematopoietic population assays by flow cytometryfound that simple forward scatter and side scatter can separate all thelineages of the hematopoietic system in the zebrafis. Erythroid,myeloid, and lymphoid cells could be separated as well as a precursorfaction. This guided transplantation of specific cell populations intomutant embryos lacking blood. GFP positive kidney marrow from a donorwas injected into these embryos that are typically bloodless. Six monthsafter the transplant, all cells in circulation were green, indicatingthat they were donor-derived. The vlad tepes and bloodless embryosappeared to be excellent hosts. In addition, secondary transplantsdemonstrated long-term reconstituting activity in the kidney marrow. Itwas also demonstrated that adult marrow could be used to rescuehematopoiesis in lethally irradiated adult zebrafish. Traver et al., 104Blood 1298-1305 (2004). This transplant protocol has been very usefulfor subsequent stem cell biology studies. See also Traver et al., 4Nature Immunol. 1238-46 (2003).

Limiting-dilution analyses of zebrafish whole kidney marrow (WKM) cellsmay show the frequency of HSCs in zebrafish kidney marrow. Because thesestudies quantify the number of transplantable stem cells, they provide afunctional assay for the comparison of stem cell function in wild-typeversus mutant zebrafish. To this end, reconstitution studies wereperformed by ablating the hematolymphoid system of an unlabeledrecipient using sublethal gamma-irradiation doses and then transplantingdilutions, ranging from 5,000 to 500,000, of GFP-labeled WKM cells intothe host. Peripheral blood was used as carrier cells in the WKM dilutionassay and served as a negative control when injected alone. After threemonths post-transplantation, the WKM was dissected from the hosts andanalyzed by flow cytometry to measure the percentage of GFP+ donor cellsin the myeloid gate. Recipients were scored as either a “success” or“failure” for donor engraftment. Using binomial maximum limitsstatistics, it was determined that the incidence of HSCs in zebrafishWKM is 1 in 61,910 cells with a 95% confidence interval between50,798-79,244 cells. This number is very similar to that of a mouse,which has ˜1 in 50,000 to 130,000 HSCs per bone marrow cell volume.Smith at al., 88 P.N.A.S. USA 2788-92 (1991). Therefore, these datasuggest that the number of stem cells in a marrow population isevolutionarily conserved.

Work has also explored the zebrafish AGM stem cell production and thenotch pathway. The AGM is thought to form from lateral mesoderm presentduring early somitogenesis. The tissue expresses flk1. As it migrates,it begins to express an artery specific marker called gridlock. Later,by eighteen somites, the cells express tie1 and tie2, and continue tomigrate medially and form a solid cord. The cord becomes hollow andturns into the aorta. At thirty hours the runx1 transcription factor isinitially expressed ventrally. Shortly after, the c-myb positivehematopoietic cells are found in the ventral wall of the aorta. Thedorsal part of the aorta expresses a T box transcription factor, calledtbx20. The process in zebrafish seems very similar to that of othervertebrates including humans, mice, chickens and frogs. Galloway & Zon,53 Curr. Topics Devel. Biol. 139-58 (2002).

The role of runx1 in the development of the AGM was also examined.Similar to the mouse knockout, a knockdown of runx1 in zebrafish led toa decreased number of cells in the AGM that are expressing c-myb.Overexpression of runx1 led to an expansion of stem cell number in theaorta, and ectopic expression of c-myb n the vein. Primitivehematopoiesis proceeds normally in the runx1 morphant. This providesevidence of a requirement of runx1 for AGM formation, and additionallyestablishes runx1 as a factor that is sufficient for generatingdefinitive stem cells. Evaluation of the role of the notch pathway inAGM formation revealed that runx1 acted downstream or parellel to notchsignaling.

The mutant mindbomb lacks an E3 ubiquitin ligase for delta, the ligandof notch receptors. As such, mindbomb mutants completely lack notchsignaling, and fail to make any hematopoietic stem cells in the AGM.Itoh et al., 4 Devel. Cell 67-82 (2003). Overexpression of runx1 rescuesthe number of c-myb positive cells in the AGM in mindbomb. This impliesthat runx is an important target of notch. In preliminary studies,adding long-acting prostaglandin E2 to the mindbomb mutant failed todemonstrate any type of rescue. This may be due to a defect in theability of the cells to respond to prostaglandin E2; notch signaling islikely to be required earlier in the development of the AGM region thanprostaglandin E2. Dose response curves with prostaglandin E2 in themindbomb mutant may shed light on this. Conversely, Notch ICD embryosthat have increased stem cell number by 36 hpf may be incubated with Coxinhibitors to see if prostaglandin signaling has a role in mediating AGMHSC upregulation. Other hematopoietic mutants may be studied similarly.

A unique transgenic system was used to examine the notch pathway. Onetransgenic line carrying the heat shock (HS) promoter driving gal4 wasmated to another line that has UAS sequences driving the intracellulardomain of notch (the activated form called NICD). Lawson et al., 128Devel. 3675-83 (2001). This provides activated notch signal to theembryo upon heat shock. Following heat shock, the AGM of these embryosshowed that c-myb and runx1 were expressed at increased intensity andover a larger area that now includes both dorsal and ventral aorta andthe vein. This ectopic expression was not accompanied by a change incell proliferation based on immunostaining with the phospho-histone H3antibody or by BrdU labeling. This fate change could be prevented byrunx1 morpholinos, formally demonstrating that runx1 acts downstream ofnotch.

Whether notch activation played a similar role in adult hematopoiesiswas studied using the double transgenic fish to conditionallyoverexpress notch. Fish were sublethally irradiated with 2000 rads, andthen subjected to heat shock, activating notch. Marrow hematopoiesis wasanalyzed by FACS for forward and side scatter, to examine myeloid,lymphoid and precursor fractions. By day seven after heat shock, theNICD expressing fish have increased myeloid and precursor fractions, andby day fourteen, there was an increase in lymphoid cells compared towildtype. Recovery following irradiation is more rapid after notchactivation. Additionally, runx1, sc1 and lmo2 are upregulated in adultsshortly after heat shock. This confirms that the notch-runx pathway thatwe discovered in embryos also operates in adult zebrafish. See Burns etal., 19(19) Genes & Devel. 2331-42 (2005)

Zebrafish have also proved useful in the characterization of diseases. Anumber of mutant fish have been developed that have the equivalent ofhuman disease. See, e.g., Dooley & Zon, 10 Curr. Op. Genet. Devel.252-56 (2000). For example, a number of membrane defects have been foundin the zebrafish system that affect erythropoiesis. Among studies,mutant genes identified were BAND 3, BAND 4.1 and spectrin.Interestingly, the BAND 3 mutant appeared to have a defect that was verysimilar to HEMPAS or CDA type 2. BAND 3 localizes to the spindle polesin the dividing erythroid precursorwhere it regulates congenital;dyserthropoietic anemia. See, e.g., Liao et al., 127(3) Devel.127(3):5123-32 (2000); Paw et al., 34(1) Nature Genet. 59-64 (2003).

Recently, grx5 was isolated as the shiraz mutant gene. Shaw et al., 440Nature 96-100 (2006). Glutaredoxin5 is located in the mitochondria andis required for iron sulfur cluster production. The mitochondrial ironimporter gene defective in the frascati mutant was also isolated, andthe frascati knock-out mouse develops anemia, similar to the fish. Seealso Donovan et al., 403 Nature 776-81 (2000); Donovan et al., 100 Blood4655-60 (2002); Wingert et al., 131(24) Devel. 6225-35 (2004); Fraenkelet al., 115 J. Clin. Invest. 1532-41.(2005); Wingert et al., 436 Nature1035-39 (2005).

As part of the Trans-NIH Zebrafish Genome Initiative, an Affymetrix chipwas designed. This involved investigation of over ten mutants affectingzebrafish hematopoieisis by studying gene expression patterns in mutantsand wild-types at different time points. Weber et al., 106(2) Blood521-30 (2005). We also have evaluated large-scale expression profilingby individual in situ hybridization screens have also been evaluated.This work has identified over 160 genes as part of the blood specificprogram.

The role of the wnt pathway in the formation of AGM HSCs and thepotential interaction with other signaling pathways known to be activein the AGM region are also relevant. Based on elegant work on the roleof the wnt pathway in HSC self renewal in adult marrow, Reya et al. 423Nature 409-14 (2003)) the wnt pathway may regulate AGM HSC production.The canonical pathway for wnt signaling involves the activation of GSKβand the subsequent translocation of β-catenin to the nucleus, where itthen interacts with one of two similar transcription factors, TCF orLEF1 to activate wnt regulated genes (FIG. 10). The wnt pathway isnegatively regulated by dickkopf and APC. The expression of wnt3stimulates a three fold in the mouse expansion of HSCs (Reya, 2003;Wilbert et al., 423 Nature 448-52 (2003)), but surprisingly the knockoutof β-catenin in HSCs does not lead to a defect in self renewal. Cobas etal., 199 J. Exp. Med. 221-29 (2004). More recent studies havedemonstrated that GSK3B inhibitors lead to a reduction in HSCdifferentiation.

Despite what is known about the action of wnt signaling in theregulation of stem cell self-renewal, there is little information aboutwnt induction of definitive stem cells in the AGM. In support of thehypothesis that wnt signaling plays a role in HSC induction, β-cateninwas identified through differential display RT-PCR methods asdifferentially expressed in the AGM region at the time of HSC formationin the mouse(REF). To define a role for wnt signaling in the AGM, thewnt pathway specific inducible lines of transgenic fish may be studied.A number of transgenic fish have been made in which the heat shockpromoter drives expression of various members of the wnt pathway.Example fish for study include: heat shock wnt8, heat shock dickkopf,and heat shock dominant-negative TCF mutants. A simple pulse of heat,similar to that utilized in the notch studies, can be used to study theeffect of wnt signaling inhibition or upregulation on AGM HSCproduction.

In an effort to better understand the role of wnt signaling in AGMformation, the heat shock wnt8 fish may be examined. wnt8 is expressedin the posterior aspect of the embryo in the tailbud region. Heat shockof the embryo between 18-22 somites led to a significant upregulation ofstem cell populations in the AGM based on runx1 and c-myb expression.The activation of wnt8 leads to expansion of stem cells, but other wntsmay similarly play a role in this process. It may be relevant todetermine which wnt proteins are expressed in the developing AGM region.CDX4+ cells will be examined by microarray analysis. Informatics may beused to examine the identity of the wnts and wnt receptors expressed inthese HSCs. Additionally, wnt 3, wnt5 and wnt8 cDNAs will be studied byin situ hybridization. Other wnts deduced from the microarrays will bestudied by ISH. A complete time course of heat shock during developmentmay localize the precise period of time in which wnt signaling isrequired for HSC formation. The heat shock dominant negative TCF andheat shock dickkopf lines to inhibit wnt signaling in the AGM may alsopbe examined. The dominant negative TCF eliminates the classical pathway,whereas the dickkopf heat shock construct inhibits both classical andnon-classical wnt pathways. Hematopoietic stem cells were completelyabsent following heat exposure of these lines. To further analyzewhether wnt is required for AGM HSC formation, several wnt agonist andantagonist chemicals may be tested, for example, by the methodsdescribed herein.

Gene expression studies following heat shock in the HS wnt8, HS dkk, andHS-DN TCF transgenic embryos are examined via expression hybridizationtechniques and Q-PCR analysis. Hematopoietic stem cell markers includingSCL, LMO2, GATA-2, GATA-1, runx1, PU.1, and ikaros may be relevant todetermine the effect of wnt signaling on the HSC population. Likewisethe expression of markers of terminally differentiated lymphoid (rag1,LCK, immunoglobulin T cell), myeloid (myeloperoxidase, L-plastin) anderythroid (erythropoietin receptor, Erb2) blood cell populations as wellas endothelial (fli1, flk1, tie2 and tie1) cells will be examinedfollowing wnt induction and inhibition. Additionally, wnt expression inthe AGM region can be monitored directly using the TOP-FLASH zebrafishline. TOP-FLASH reporter fish express GFP under an inducible promotermade of multimerized LEF1 binding sites. Dorsky et al., 241 Devel. Biol.229-37 (2002). The reporter is known to be active in posterior mesodermformation. It is likely that cdx4, described previously, is emulated bywnt. The expression of the TOP-FLASH reporter may be examined in depthin the developing AGM region. The wnt pathway heat shock fish is usefulto further investigate the role of wnt signaling in adult marrowhomeostasis. Evaluating kidney marrow recovery following irradiation inthe HS wnt8 and HS-DN TCF transgenic fish would decipher the requirementfor wnt signaling in HSC proliferation and maintenance. In addition,limiting dilution and competitive repopulation studies with heat shockinduced marrow compared to normal marrow are useful.

The relationship of the wnt and notch pathways with the prostaglandininduction of AGM stem cells may also be important in hematopoeisis. Theembryonic phenotypes of notch loss of function and wnt loss of functionare very similar, with both leading to a dramatic deficiency of AGM stemcells. This leads to the hypothesis that one pathway may cross regulatethe other. We plan to evaluate whether the heat shock wnt8 constructwill rescue the mindbomb mutant and similarly whether the dominantnegative TCF mutant can be rescued by activating notch ICD. This type ofanalysis should lead to a better understanding of the precise timing ofactivation of these pathways during embryogenesis. It will also allow usto understand more about the interaction of these pathways. Mutant fish(and/or morpholino injected fish) may also be used to combine with notchand wnt deficiencies as well as gain of function phenotypes. Molecularmarker examination as describe above and for Notch characterizationshould establish if both pathways cooperate to regulate stem cellinduction and/or stem cell proliferation, renewal, and differentiation.

Members of the wnt pathway have been shown to interact withprostaglandins. For instance, for colon cancer models induced by wnt,nonsteroidals that block Cox1 or 2 prevent cancer formation. Asdescribed above, PGE2 leads to an increase in stem cells in the AGM.PGE2 may rescue wnt deficient embryos. COX2 inhibitor may block theeffects of HS-wnt8. Other HSC modifiers encompassed by the presentinvention include Wnt pathway modifiers. Example Wnt pathway modifiersfound to inhibit HCSs were Kenpaullone (HDAC effect, not GSK3b), andValproic Acid (HDAC effect, not GSK3b). HSC enhancers found to modifythe Wnt pathway were lithium chloride and BIO.

Using transgenic zebrafish expressing activators or repressors of wnt,the effects of wnt signaling on the development of HSCs in theaorta-gonad-mesonephros (AGM) region were examined. Induction of wntsignaling led to enhanced HSC formation, while inhibition reduced HSCproduction. In adult zebrafish, increased wnt activity enhancedprogenitor cell number during kidney marrow recovery followingirradiation. Because (PG) E2 regulates HSC formation and homeostasis invertebrates, the interaction of the wnt and PG pathways during HSCdevelopment and in marrow recovery was explored by exposing TOP:dGFPembryos to drugs that regulate prostaglandin signaling. Dimethyl-PGE2(dmPGE2), a potent inducer of HSC formation, was found to enhance wntsignaling, while the cyclooxygenase inhibitor indomethacin (indo),resulted in the virtual absence of wnt activity. Inhibition of HSCformation by wnt repression was partially rescued by dmPGE2 treatment,while induction of HSCs by overexpression of wnt was reversed by indoexposure. Indo also blocked the wnt-mediated increase in kidney marrowprecursors following irradiation in adult fish. PGE2 induced wntactivity in the AGM of TOP:gal mice, indicating the molecularconservation of the wnt and PG interaction and the role of wnt in HSCformation.

More specifically, Wnt signaling through its main transcriptionalmediator β-catenin plays an important role in controlling tissuepatterning, cell fate decisions, and proliferation in many embryoniccontexts, including the development and differentiation of organs. SeeFIG. 10. Wnt activity has been shown to increase adult HSC self-renewaland enhance stem cell repopulation following HSC transplantation intoNOD/SCID mice. β-catenin was also found to be differentially expressedin the AGM regions in mouse embryos at e10-12. Whether wnt signaling hasa role during HSC formation in zebrafish was determined using heat shockinducible activators and repressors of the wnt pathway. Briefly,wnt-inducible embryos were harvested and heat shocked for twenty minutesat 38° C. Genotypes were sorted by GFP expression, and the AGM HSCsanalyzed by runx1/cmyb expression in situ. Induction of wnt8 by heatshock at five somites led to increased HSC formation in the AGM at 36hpf, while abrogation of wnt signaling by induction of dkk and dnTCFsignificantly inhibited runx1/cmyb expression. This is the firstevidence in any organism that wnt signaling is required for AGM HSCformation.

An irradiation recovery assay was also employed to investigate the roleof wnt signaling in hematopoietic homeostasis in zebrafish. Transgenicfish expressing wnt-related genes were sublethally irradiated and heatshock gene induction was initiated by overnight incubation at 38° C. onday two post-irradiation. Kidney marrow was harvested at varioustimepoints post-irradiation as outlined previously for the prostaglandinexperiments. FIG. 11. Utilizing the heat shock wnt8 fish demonstratedthat an increase in the precursor population compared to controls on dayten post irradiation, similar to that seen with PGE2. Inhibition of wntsignaling, by heat shock dkk or dnTCF, drastically alters the kineticsof marrow recovery and can result in the complete failure of marrowregeneration and lethality.

Clinical experience in patients with APC mutations has shown thatinhibition of prostaglandin synthesis results in decreased wnt mediatedpolyp formation. Furthermore, recent studies in colon cancer cell linessuggest an interaction between the prostaglandin and wnt signalingpathway. These interactions were examined in vivo using a wnt reporterzebrafish transgenic line, TOP:dGFP. At fifty-percent epiboly, embryoswere subjected either to nothing (control), indomethacin, or PGE2, andthe amount of wnt signaling activated in the embryo assessed by GFPinduction driven from the wnt binding site. Analysis of alterations inGFP expression in the head was analyzed by in situ hybridization.Compared to the control, PGE2 treatment markedly enhanced wnt activity,while indomethacin severely reduced GFP expression. FIG. 12. These datacomprise the first in vivo documentation of the interaction of the wntand prostaglandin pathways during embryonic development.

Additionally, indomethacin and dmPGE2 was used to investigate theinteraction of the wnt and prostaglandin pathways during HSC developmentand in marrow recovery following injury. FIG. 13 reflects the potentialpoints of interaction of the PG and wnt pathways. The wnt-mediatedenhancement of runx1/cmyb expression in wnt8 embryos heat shocked atfive somites can be blocked by treatment with indomethacin. Furthermore,dmPGE2 can rescue the inhibitory effects of dkk activation on AGM HSCformation at 36 hpf, as shown by in situ hybridization for runx1/cmyb.Preliminary results show the dmPGE2 treatment is not sufficient,however, to rescue HSC formation in embryos over-expressing dnTCF.

To determine if prostaglandin pathway manipulation can alter wntactivity in the kidney marrow repopulation in the adult, the effects ofdmPGE2 and indomethacan was examined further in Top:dGFP lines. DmPGE2significantly enhanced wnt activity on day three post irradiation, whileindomethacin inhibited GFP expression. FIG. 14. To discern whethermodulation of prostaglandin signaling can modify the wnt mediatedeffects on kidney marrow recovery following irradiation, wnt genes wereactivated by heat shock at 38° C. at two days post irradiation and then.exposure to prostaglandin pathway drugs at one day post heat shock. Thehs:wnt8-GFP fish were exposed to indomethacin, while the dkk1, axin, anddnTCF transgenic fish were exposed to dmPGE2. Whole kidney marrow wasanalyzed by FACS on day ten post-irradiation. Treatment withindomethacin was observed to severely diminish the wnt-mediatedenhancement in the precursor cell population, suggesting that PGE2levels can directly modulate wnt-signaling in vivo.

These experiments suggest that pharmacological manipulation of wntactivity through modulation of PG signaling will provide a novel meansfor therapeutically regulating HSC homeostasis.

Several embodiments will now be described further by non-limitingexamples.

EXAMPLES Example 1 Chemical Screen Design and Confirmatory Testing

Wild-type age-matched embryos were arrayed into 48-well plates (-5embryos/well) of individual test compounds and exposed from 3-somitesuntil 36 hpf. Three compound libraries were utilized: NINDS CustomCollection (1040), SpecPlus Collection (960) and BIOMOL ICCB KnownBioactives (480). Five percent (123/2480) of the compounds were toxic,resulting in death or severe morphological abnormalities. In situhybridization for runx1 and cmyb was performed to assess HSCs. Compoundswere retested at 10 □M, 20 □M, and 50□M. Stem cell specificity wasassessed using flk1 at 36 hpf. PGE2, PGI2, dmPGE2 and all cox inhibitors(Sigma) were used at 10 □M to 20 □M.

Qualitative scoring (# embryos with altered HSCs/# scored) of runx1/cmybwas conducted using the following criteria: Normal/unchanged=continuousline of runx1/cmyb+ endothelial cells and occasional hematopoieticclusters. Decreased/absent=reduction in runx1/cmyb+ cells, including thepresence of large gaps in the line of HSCs, isolated positive cells, orabsence of expression. Increased/excess=enhancement in runx1/cmyb⁺cells, including many HSC clusters, a thickened line of HSCs, or ectopicexpression.

Confocal Imaging

Live 36 hpf treated bigenic zebrafish embryos were embedded in 1%low-melting point agarose containing 0.4 mg/ml Tricaine-S for confocalimaging. cmyb-GFP transgenic reporter lines were created from a BACcontaining the cmyb promoter genomic sequence (Galloway, Zhu, Lin, Zon,unpublished); lmo2:DsRed fish were created as described²⁷. For HSCquantification, cmyb/lmo2+ positive cells were counted in projections ofz-stack images (n=10/treatment).

Morpholino Knockdown [000143] Morpholino oligonucleotides (GeneTools)directed against zebrafish cox1 and cox2, PGE2 synthase, and EP2 and EP4(Grosser et al., 2002; Cha et al., 2006, Pina et al., 25 Arterioscler.Thromb. Vasc. Biol. 315-20 (2005)), were injected (40 μM) into zebrafishembryos at the one-cell stage. For rescue experiments, 3-somite stageMO-injected embryos were exposed to 10 μM dmPGE2.

Microarray Gene Expression Profiling

gata1:GFP (12 somites), lmo2:GFP (12 somites and 35 hpf) and cd41:GFP(35 hpf) positive cells were FACS-sorted; total RNA was purified andanalyzed using Affymetrix zebrafish gene chips as described previously.Weber et al., 106 Blood 521-30 (2005).

Quantitative PCR

qPCR was performed using previously described primer sets. Burns et al.,19 Genet Devel. 2331-42 (2005). Embryos (n=50) were treated asdescribed. qPCR (60° C. annealing) was performed using SYBR GreenSupermix on the iQ5 Multicolor RTPCR Detection System (BioRad) (n=10replicates) and relative expression levels were determined. Primer pairsfor EP2 and EP4 were determined by methods well known in the art. qPCRof whole KM RNA (n=15/variable) was performed on day threepost-irradiation as described. Burns et al., 19 Genes Devel. 2331-42(2005). qPCR on S cell RNA (harvested in Stat-60, Tel-Test) wasperformed using the Stratagene Sybrgreen kit on the Stratagene qPCRmachine. PG primer sequences were determined by methods well known inthe art.

Mass Spectroscopy

PGE₂ and the stable PGI₂ metabolite, 6-keto-PGF_(1α), were measuredusing HPLC-tandem mass spectrometry. Ethylacetate extracts fromhomogenized embryos were spiked with the corresponding stable isotopelabeled internal standards (d₄-PGE₂ and d₄-6-keto PGF_(1α)) and allowedto react with methoxylamine. The following mass transitions weremonitored: m/z 384→272 (PGE), m/z 398→368 (6-keto PGF_(1α), and TxB2).

Radiation Recovery Assay

Adult zebrafish were exposed to 23 Gy of γ-irradiation. On day twopost-irradiation, fish were exposed overnight to DMSO control, dmPGE2(10 or 50 μM), Indomethacin (10 μM), SC560 (10 μM) or NS398 (10 μM) infish water. Whole KM isolated on days 0, 2, 4, 7, 10, 14 was subjectedto FSC/SSC FACS analysis to identify hematopoietic lineages(n=5/treatment×3 replicates). Traver et al., 104 Blood 12980305 (2004).

ES cell Differentiation Assays

ES cell hematopoietic differentiation assays were performed aspreviously described. Kyba et al. 100(1) P.N.A.S. USA 11904-10 (2003);Wang et al., 102 P.N.A.S. USA 19081-86 (2005). dmPGE2 (10, 20 or 100 μM)or indomethacin (20, 100 μM) were added at day four and day five duringEB expansion. M3434 methylcellulose colony forming and OP9 colony assayswere conducted on day 6 and analyzed at days 8 and 5, respectively.Colony type was identified by morphological analysis; duplicate chemicalexposures were averaged to determine the reported colony number (n=3replicates minimum).

Murine Colony-Forming Units-Spleen (CFU-S)

WBM cells from the femurs of 8-week old C57B1/6 mice were incubated exvivo with (1 μM/106 cells) dmPGE2, indomethacin, SC560, NS398 or EtOHcontrol on ice for two hours. Two independent BM samples were treated(n=5/treatment×2 replicates) for each variable. Recipient mice werelethally irradiated with a split dose of 10 Gy. 6×10⁴ unfractionateddmPGE2 or control-treated BM cells were injected retro-orbitally intoirradiated recipient mice. Spleens were dissected on day eight ortwelve, weighed and fixed with Bouin's solution; hematopoietic coloniesper spleen were counted. 1×10⁵ cells/recipient were transplanted aftertreatment with the cox inhibitors. FACS sorted ckit⁺ sca1⁺lineage⁻ BMcells were treated as above and transplanted at a dose of either100cells/recipient or 300 cells/recipient.

5-Fluorouracil Bone Marrow Injury

Mice were treated with 5-FU (150 mg/kg) as described. Venezia et al.,2004. SC560, NS398, dmPGE2 (1 mg/kg) or EtOH control were administeredby IP injection on days 1, 5, 9, 13, and 17 post injection. Peripheralblood was obtained on day seven and day fourteen, quantified andsubjected to multilineage FACS analysis using antibodies (eBioscience)to B220/IgM (B-lymphoid), CD4/8 (T-lymphoid), Mac1/Gr1 (myeloid),Ter119/CD71 (erythroid) and ckit/scal (stem/progenitor). Mice weresacrificed on day 16, and bone marrow was isolated, quantified andanalyzed by FACS.

Limiting Dilution Competitive transplantation

WBM from CD45.1 C57B1/6 mice was incubated with dmPGE2 or EtOH controlex vivo as described. Treated-test cells were independently transplantedinto irradiated CD45.2 recipients (n=5/variable×2) with untreatedCD45.1/CD45.2 competitor at the following ratios: 15,000:200,000(0.075:1), 50,000:200,000 (0.25:1), 200,000:200,000 (1: 1),2,000,000:200,000 (10:1). Peripheral blood (PB) was obtained at six,twelve, and twenty-four weeks post-transplantation, and white bloodcells were FACS-analyzed to determine test reconstitution for eachseries of treatment populations. Frequency of PB chimerism>5% was usedto calculate the number of repopulating cells using the L-Calc program(Stem Cell Technologies). For twelve-week and twenty-four-week PBsamples, multilineage reconstitution was measured by FACS analysis asabove.

Example 2 Additional HSC Modulators

Zebrafish embryos were screened as described above. Another group of HSCmodifiers identified by the techniques described herein and encompassedby the present invention are cAMP/P13K/AKT second messenger modifers,which may be downstream of PG signaling. Those which inhibit HCS includePD9805, KT5720, H89, U0126, and Wortmannin. Those which enhance HSCinclude 8-bromo-cAMP and Forskolin.

Another group of HSC modifiers that may also act downstream of PGsignaling are Ca2+ second messenger modifiers. These include HSCinhibitors and HSC enhancers listed in Table 9:

TABLE 9 Example Ca2+ second messenger modifiers HSC Inhibitors HSCEnhancers BayK 8644 Bapta-AM Thioridazine Fendiline Nicardipine PimozideStrophanthidin Lanatoside

A further group of HSC modifiers identified by the screening techniquesdescribed herein and encompassed by the present invention areNO/Angiotensin signaling modifiers, which may interact with PG and wntsignaling. These include HSC inhibitors and HSC enhancers listed inTable 10:

TABLE 10 Example NO/Angiotensin signaling modifiers HSC Inhibitors HSCEnhancers L-NAME L-Arg Enalapril Sodium Nitroprusside Captopril SodiumVanadate AcSDKP Bradykinin Losartan Telimasartan Histamine AmbroxolChrysin Cycloheximide Methylene Blue Epinephrine Dexamethazone ProadifenBenzyl isothiocyanate Ephedrine

The zebrafish screening methods of the present invention were alsoapplied to identify other HSC modulators whose interactions with PG orwnt signaling are presently unclear. These compounds, also encompassedby the present invention, include those with either inhibit or enhanceHCSs as indicated in Table 11:

TABLE 11 Example HSC modulators. HSC Inhibitors HSC Enhancers ParagylineMebeverine Propranolol Flurandrenolide Etanidazole Atenolol MethimazolePindolol Cinoxacin Gaboxadol Penicillamine Kynurenic Acid FurosemideHydralazine Eburnamininone Thiabendazole Aclarubicin Bicuclline WarfarinVesamicol Gamma-aminobutyric Acid Peruvoside Norethindrone ImipramineLupinidine Chlorpropamide Hydroquinidine 1,5-PentamethylenetetrazoleTodralazine 4-Aminopyridine Methoxamine Diazoxide HydroxyureaBenfotiamine Dihydroergotamine 12-Methoxydodecenoic acid AntazolineN-Formyl-Met-Leu-Phe 3-Nitropropionic Acid Gallamine N-PhenylanthranilicAcid IAA 94 Phenazopyridine Chlorotrianisene Dichlorokynurenic acid3-estradiol L-Leu Phenoxybenzamine Mephentermine Guvacine GuaiazuleneImidazole Beta-Carotene Clofibrate

1. A method for promoting hematopoietic reconstitution in a humansubject, comprising contacting a population of human hematopoietic stemcells (HSCs) ex vivo with an HSC modulator to promote hematopoieticreconstitution in the subject and administering the contacted HSCs tothe subject, wherein the HSC modulator is a prostaglandin E₂ (PGE₂)receptor agonist.
 2. The method of claim 1, wherein the PGE₂ receptoragonist is selected from the group consisting of a prostaglandin E2receptor-1 (EP-1) agonist, a prostaglandin E2 receptor-2 (EP-2) agonist,a prostaglandin E2 receptor-3 (EP-3) agonist and a prostaglandin E2receptor-4 (EP-4) agonist.
 3. The method of claim 1, wherein the HSCmodulator is selected from the group consisting of: PGE₂, prostaglandinI₂ (PGI₂), 16-phenyl tetranor PGE₂, 16,16-dimethyl PGE₂, 19(R)-hydroxyPGE₂, 16,16-dimethyl PGE₂ p-(p-acetamidobenzamido) phenyl ester,9-deoxy-9-methylene-16,16-dimethyl PGE₂, PGE₂ methyl ester, Butraprost,15(S)-15-methyl PGE₂, 15(R)-15-methyl PGE₂, 11-deoxy-16,16-dimethylPGE₂, 9-deoxy-9-methylene PGE₂, PGE₂ serinol amide, and Sulprostone. 4.The method of claim 1, wherein the hematopoietic reconstitutioncomprises multilineage hematopoietic reconstitution in the subject. 5.The method of claim 1, wherein the hematopoietic reconstitutioncomprises reconstitution of long-term hematopoietic stem cells in thesubject.
 6. The method of claim 1, wherein the hematopoieticreconstitution comprises reconstitution of short-term hematopoietic stemcells in the subject.
 7. The method of claim 1, wherein the populationof human HSCs is obtained from peripheral blood, cord blood, bonemarrow, amniotic fluid, or placental blood.
 8. The method of claim 1,wherein the population of human HSCs is obtained from peripheral bloodor cord blood.
 9. The method of claim 1, wherein the subject is acandidate for bone marrow or stem cell transplantation, or the subjecthas received chemotherapy or irradiation therapy.
 10. The method ofclaim 1, wherein the subject has a solid tumor, myeloma, or lymphoma.11. The method of claim 1, wherein the subject has anemia.
 12. Themethod of claim 11, wherein the anemia is sickle cell anemia,thalassemia, or aplastic anemia.
 13. The method of claim 1, wherein thesubject has a hyperproliferative disorder of the hematopoietic system.14. The method of claim 13, wherein the hyperproliferative disorder ofthe hematopoietic system is polycythemia vera, essentialthrombocythemia, myelofibrosis with myeloid metaplasia, or chronicmyelogenous leukemia.
 15. The method of claim 1, wherein the populationof human HSCs is cryopreserved.
 16. The method of claim 1, wherein thepopulation of human HSCs is cryopreserved prior to contacting thepopulation of cells with the HSC modulator ex vivo.
 17. The method ofclaim 1, wherein the HSC modulator comprises 16,16-dimethyl-PGE₂. 18.The method of claim 1, wherein the population of human HSCs isautologous to the subject.
 19. The method of claim 1, wherein thepopulation of human HSCs is allogeneic to the subject.
 20. The method ofclaim 1, wherein the contacted population of human HSCs is administeredintravenously to the subject.